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Audenz™ Avian Influenza H5N1 (Bird Flu) Vaccine Clinical Trials, Dosage, Efficacy, Indication, Side Effects

CSL Seqirus Inc. Audenz™ (aH5N1c) (STN: 125692) is a monovalent, adjuvanted, cell-based inactivated subunit vaccine designed to protect people from disease caused by the influenza A virus H5N1 subtype in the event of avian influenza pandemics. During H5N1 bird flu pandemics, a lack of preexisting immunity to novel influenza strains increases morbidity and mortality. Audenz is a milky-white sterile injectable emulsion prepared from a virus propagated in Madin Darby Canine Kidney cells for intramuscular use.

Audenz's initial U.S. Food and Drug Administration (FDA) Approval was in January 2020 for use in persons six months and older, and it received  Supplemental FDA approval in 2021. Clinical safety data for AUDENZ in adults have been collected from three studies: Study 1 in adults 18 through 64 years of age (NCT01776541); Study 2 in adults 65 years of age and older (NCT01766921), and Study 3, a placebo-controlled trial in adults 18 years of age and older (NCT02839330). Subjects in all studies received two doses of AUDENZ, administered intramuscularly 21 days apart. Limited adverse events were detected.

CSL Seqirus has produced zoonotic vaccines to address the H5N1 threat using egg-based technology at its Liverpool, UK facility (virus grown in eggs) and cell-based technology at its Holly Springs, NC facility (virus grown in cells). The Holly Springs, NC, facility was built through a public-private partnership established in 2009 with BARDA. It is the world's largest cell-based influenza vaccine producer and the first such domestic facility.

Both technologies utilize CSL Seqirus' MF59®-adjuvanted technology and have been proven capable of producing vaccines against various strains of pandemic potential. The current egg-based adjuvanted zoonotic vaccine is based on the approved Aflunov platform, while the cell-based adjuvanted zoonotic vaccine is produced based on the approved Audenz platform.

The journal Vaccines confirmed on December 11, 2021, four studies (total N = 6,230) assessed the immunogenicity and safety of mammalian cell-based, MF59®-adjuvanted, A/H5N1 vaccine (aH5N1c; AUDENZ) as two doses administered on Days 1 and 22 in children (NCT01776554), adults (NCT01776541; NCT02839330), and older adults (NCT01766921; NCT02839330). Overall, an age-related response was evident, with the highest responses observed in children <3 years old. In children, antibody titers met seroconversion criteria 12 months after vaccination.

On March 23, 2022, a peer-reviewed study published by the journal Vaccines reported that 'A cell-based process' may be better suited for vaccine production during an HPAI pandemic; the aH5N1c influenza vaccine (Audenz) elicited high levels of antibodies following two vaccinations administered 21 days apart and met immunogenicity criteria at Day 43 among both younger and older adults with a clinically acceptable safety profile. The consistency of the three consecutive aH5N1c vaccine lots was demonstrated in a phase 3 study.

Seqirus has a five-year agreement with the Biomedical Advanced Research and Development Authority (BARDA), a division of the Assistant Secretary for Preparedness and Response Office (ASPR) within the U.S. Department of Health and Human Services, to supply products. Avian influenza vaccines ensure that people can be vaccinated as directed by the U.S. National Influenza Vaccine Modernization Strategy and the American Pandemic Preparedness Plan. On June 2, 2022, the U.S. government confirmed that Seqirus has established and will maintain the required pandemic readiness to deliver 150 million doses of a cell-based pandemic influenza vaccine within six months of an influenza pandemic declaration in the U.S. During a bird-flu pandemic in the U.S., BARDA would source vaccines from the CSL Seqirus Holly Springs, NC facility in a pandemic. BARDA certified this facility in June 2022. The product is not marketed directly to consumers or available through traditional retail channels.

An alternative to traditional egg-based manufacturing, cell-based manufacturing avoids egg-adapted changes, one source of strain mismatch between the vaccine and circulating pandemic influenza virus. The antigen is stockpiled and, in the event of an influenza A (H5N1) pandemic, would be rapidly formulated into doses for the U.S. government. Audenz combines Seqirus's proprietary MF59® adjuvant technology with its cell-based manufacturing platform. Access to pre-pandemic vaccines using either cell- or egg-based manufacturing technologies from SeqSeqirus'sobal production facilities, including Holly Springs, North Carolina; Liverpool, United Kingdom; and Parkville, Australia.

As of 2024, the U.S. Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO) consider the current risk to the general public from the ongoing H5N1 outbreak in wild birds, poultry, and mammals to be low. The WHO published the Pandemic Influenza Pandemic Framework's partnership Contribution High-Level Implementation Plan III, which outlines the strategy for strengthening global pandemic influenza preparedness from 2024 to 2030.

U.S. FDA STN: 125692; BLA Approval; Supplemental Approval Letter: BL125692/18; Package Insert. There is no postmarketing experience following the administration of AUDENZ, and no data are available to evaluate the concomitant administration of AUDENZ with other vaccines. There is insufficient data on AUDENZ in pregnant women to inform vaccine-associated risks in pregnancy.

New Jersey-based CSL Seqirus is a global leader in influenza prevention (ASX: CSL). Its trademark is 88789443.

Audenz Vaccine Indication

Audenz is indicated to protect individuals six months of age and older against influenza A(H5N1) in a pandemic. Do not administer AUDENZ to anyone with a history of a severe allergic reaction (e.g., anaphylaxis) to any vaccine component or after a previous dose of an influenza vaccine. 

Audenz Vaccine Dosage

Audenz is administered as an intramuscular injection. It is given in two doses, .5 ml each, 21 days apart. The U.S. FDA approved a multi-dose vial presentation for Audenz on November 23, 2021.

Audenz Vaccine Immunocompromised

Immunocompromised persons, including those receiving immunosuppressive therapy, may have a diminished immune response to AUDENZ.

Audenz Vaccine Side Effects

In adults 18 through 64 years of age, the most common (≥ 10%) solicited local and systemic reactions reported in clinical trials were injection site pain (64%), fatigue (25%), and headache (25%). Avoid use if there is any history of a severe allergic reaction (e.g., anaphylaxis) to any vaccine component or after a previous dose of an influenza vaccine. To report SUSPECTED ADVERSE REACTIONS, contact Seqirus at 1855358, VAERSAERS at 1800822,7,967, or www.vaers.hhs.gov. 

Audenz Vaccine Serious Adverse Events

In Clinical Study 3, the FDA disclosed fatal and non-fatal SAEs reported in the 12 months following vaccinations among adults 18 through 64 years of age occurred in 2.9% of subjects who received AUDENZ and 3.3% of subjects who received placebo. SAE rates among adults 65 and older were 10.5% in subjects administered AUDENZ and 15.3% in subjects who received a placebo. Fatal SAEs included 11 (0.5%) AUDENZ recipients and 1 (0.1%) placebo recipients. No SAEs were assessed as being related to AUDENZ. Studies 1 and 2 did not have a placebo or active comparator control for safety comparison. Four deaths occurred in Study 1 (subjects 18 through 64 years) and two in Study 2 (subjects ≥ 65 years), none assessed as related to AUDENZ. In the 12 months following vaccinations, SAEs (fatal and non-fatal) occurred in n=28 (3%) of all subjects in Study 1. SAEs occurred in a total of n=96 (7%).

Pandemic Influenza Vaccines

Pandemic influenza occurs when a new flu virus emerges for which humans have little or no immunity, allowing the virus to spread rapidly from person to person worldwide. Under the terms of an agreement in May 2024, CSL Seqirus will deliver approximately 4.8 million pre-pandemic vaccines matched to the H5 of the currently circulating H5N1 strain. This is the fourth award CSL Seqirus has received from BARDA.

Audenz Vaccine News

October 4, 2024 - "Pandemic preparedness is a core part of who we are," said Jon Kegerise, Vice President of Manufacturing and Site Head at CSL Seqirus Holly Springs. "Our Holly Springs site was built to deliver innovative pandemic solutions at industrial scale and speed."

May 16, 2024 - Do We Have Enough Bird Flu Vaccines for a Potential Pandemic?

June 14, 2023 - The U.S. CDC published H5N1 Bird Flu: Current Situation Summary.

April 14, 2023—The United States Department of Agriculture's Agricultural Research Service researchers are testing several vaccine candidates. Initial data from the animal study with a single dose of the vaccine are expected to be available in May 2023. The researchers expect two-dose vaccine challenge studies with results in June 2023.

December 21, 2022 - The UKHSA published an original Research and Analysis investigation into the risk to human health of avian influenza (influenza A H5N1) in England: technical briefing #1.

July 29, 2022 - "It is best practice never to touch or handle deceased birds or exhibit signs of distress or illness," says Dr. Sundari Mase, Sonoma County health officer. "While severe cases of bird flu are possible in humans, we rarely see symptoms develop beyond those of the common cold."

J "ne 2, 2022 - CSL Seqirus announced its facility in Holly Springs, North Carolina. As the Biomedical Advanced Research and Development Authority outlined, it has achieved all the criteria to establish domestic manufacturing capability for cell-based seasonal and pandemic influenza vaccines.

May 26, 2022: The journal Nature published "Why unprecedented bird flu outbreaks sweep the world," which concerns scientists.

May 17, 2022 - The U.S. CDC recently added the Eurasian H5N1 avian flu strain to the list of animal flu viruses with zoonotic potential.

April 2022—The United States Department of Agriculture's Animal and Plant Health Inspection Service confirmed the presence of HPAI in a commercial pheasant flock in Erath County, Texas, to confirm a HAPI outbreak in 2022.

February 25, 2022 - Seqirus announced the renewal of a five-year agreement with the BARDA, a division of the Office of the Assistant Secretary for Preparedness and Response. This agreement empowers BARDA to request that Seqirus provide influenza vaccines and adjuvants for pre-pandemic stockpiling or manufacture to support rapid response to an influenza pandemic or other public health emergency. Seqirus and BARDA have held similar agreements since 2006.

November 23, 2021: The FDA has approved AUDENZ's multi-dose vial presentation to help protect individuals six months of age and older against influenza A(H5N1) during a pandemic.

October 4, 2021 - Seqirus announced that the Biomedical Advanced Research and Development Authority selected Seqirus to develop two influenza A(H2Nx) vaccine candidates for assessment in Phase 1 clinical study to help safeguard communities in the event of an influenza pandemic. The first candidate will utilize cell-based and adjuvanted technologies, building on SeqSeqirus'sghly flexible combination platform technology used by AUDENZ.

February 3, 2020 - Seqirus Announces U.S. FDA Approval of Its First Adjuvanted, Cell-Based Pandemic Influenza A (H5N1) Vaccine.

January 31, 2020 - The FDA approved Seqirus' Biologics License Application for Influenza A (H5N1) Monovalent Vaccine, Adjuvanted effective in persons six months and older. For use in persons six months through 17 years of age, the FDA has approved the BLA according to the regulations for accelerated approval, 21 CFR 601.41.

Audenz Influenza A(H5N1) Vaccine Clinical Trials

Audenz has been studied in various clinical trials.

Ivermectin

Ivermectin (STROMECTOL®) is a U.S. Food and Drug Administration (FDA) approved semisynthetic, anthelmintic agent for oral administration. Ivermectin is derived from the avermectins, a class of highly active, broad-spectrum, antiparasitic agents isolated from the fermentation products of Streptomyces avermitilis. Ivermectin is a mixture containing at least 90% 5-Odemethyl-22,23-dihydroavermectin A1a and less than 10% 5-O-demethyl-25-de(1-methylpropyl)-22,23-dihydro25-(1-methylethyl)avermectin A1a, generally referred to as 22,23-dihydroavermectin B1a and B1b, or H2B1a and H2B1b, respectively.

On March 6, 2023, the FDA confirmed that Ivermectin is an approved antiparasitic drug used to treat several neglected tropical diseases, including onchocerciasis, helminthiases, scabies, and strongyloidiasis, all of which are caused by parasitic worms. Ivermectin has been widely used for these indications and is generally well tolerated. Ivermectin is usually well tolerated when used at appropriate doses for approved indications.

Ivermectin Indication

The U.S. CDC states that Ivermectin is indicated for the treatment of the following infections: Strongyloidiasis of the intestinal tract. Ivermectin is indicated for treating intestinal (i.e., non-disseminated) strongyloidiasis caused by the nematode parasite Strongyloides stercoralis. This indication is based on clinical studies of comparative and open-label designs, in which 64-100% of infected patients were cured following a single 200-mcg/kg dose of Ivermectin.

In addition, some topical forms of Ivermectin are approved to treat external parasites, such as head lice, and skin conditions like rosacea. Zydus Lifesciences Limited (formerly Cadila Healthcare Limited) received final approval from the USFDA to market Ivermectin Cream, 1% (Soolantra). Ivermectin Cream is used the treat inflammatory lesions of rosacea. Soolantra will be manufactured at the group's topical manufacturing facility in Ahmedabad, India.

Ivermectin is contraindicated for those five years of age or those weighing less than 15 kilograms and individuals with liver or kidney disease.

ivermectin Scabies

The results of a multicenter trial indicate that Ivermectin can be safely used in young children for scabies treatment. "Outcomes from the Ivermectin Safety in Small Children trial will hopefully provide greater reassurance that ivermectin can be safely used in children weighing less than 15 kilograms," lead study author Kevin Kobylinski, PhD, a University of Oxford honorary visiting research fellow with the Mahidol Oxford Tropical Medicine Research Unit in Bangkok, said in a press release on November 10, 2025.

Ivermectin Malaria

A study published in the New England Journal of Medicine on July 23, 2025, concluded that Ivermectin reduced the incidence of malaria by 26% in a cluster-randomized trial (BOHEMIA) conducted in Kenya, Africa. Previously, The Lancet published the results of a 2019 study. The primary analysis of this study revealed that the mean number of clinical malaria episodes per child was approximately 20% lower in the intervention group than in the control group during the 18-week treatment period. Two groups of clusters (three in Mozambique) were randomized to receive (a) ivermectin in humans, (b) ivermectin in humans + livestock (only in Mozambique), or (c) albendazole control. WHO's PPC states that the desired efficacy of an endectocide as stand-alone insecticide in areas of high to moderate transmission is at least 20% reduction in the incidence of clinical malaria (as primary outcome) and incidence of infection (as secondary outcome) in children under 5 years old (the highest incidence age-group in areas with high-transmission), lasting for at least 1 month following a single regimen.

Ivermectin Dengue

Ivermectin has been previously shown to inhibit all four dengue serotypes in vitro by blocking the host nuclear import proteins that are crucial for the nuclear localization of the dengue NS5 protein, which has RNA-dependent RNA polymerase (RdRp) function. A phase 2/3 randomized, double-blind, placebo-controlled trial (NCT02045069) was conducted to study the efficacy of a once-daily dose of Ivermectin 400 μg/kg for 2–3 days in adult dengue patients. Interestingly, the study reported faster NS1 antigenemia clearance upon ivermectin treatment, with no difference in viremia, viral clearance, or any beneficial clinical outcomes, including fever, DHF incidence, hospitalization, pleural effusion, hemoconcentration, or fluid requirements.

Ivermectin Use Against Human Adenoviruses

Human adenoviruses (HAdVs) are ubiquitous and clinically essential pathogens without an effective antiviral treatment. HAdV infections typically cause mild symptoms; however, individuals such as children, those with underlying conditions, and those with compromised immune systems can develop severe disseminated disease. One study found that Ivermectin, an FDA-approved antiparasitic agent, effectively inhibits the replication of several HAdV types in vitro.

Ivermectin Clinical Trials

Ivermectin (Stromectol, Mectizan) has been tested in over 190 clinical trials.

ABRYSVO™ RSV Vaccine Clinical Trials, Dosage, Efficacy, Indication, Side Effects

Pfizer Inc.'s ABRYSVO™ RSVpreF (PF-06928316) bivalent prefusion F subunit vaccine is a U.S. Food and Drug Administration (FDA) approved vaccine (STN: 125769; 125768) based on the crystal structure of prefusion F, a vital form of the viral fusion protein (F) that respiratory syncytial virus (RSV) uses to attack human cells. The vaccine comprises two preF proteins selected to optimize protection against RSV A and B. ABRYSVO builds on foundational basic science discoveries, including those made at the U.S. National Institutes of Health (NIH), which detailed the crystal structure of a critical viral protein that RSV uses to attack human cells. 

ABRYSVO is indicated to prevent RSV infections and hospitalizations in adults and infants. For infants, ABRYSVO is designed to stimulate the production of serum anti-F immunoglobulin G in the pregnant mother, which can then be transferred to the fetus across the placenta and protected for the first six months of life when the risk of hospitalization is highest. For seniors (60 years+), the ABRYSVO vaccination prevents acute respiratory disease and lower respiratory tract disease (LRTD) caused by RSV. On August 21, 2023, the FDA approved Abrysvo for use in pregnant women to prevent LRTD and severe LRTD caused by RSV in infants from birth through six months. On September 22, 2023, Abrysvo was approved by the U.S. CDC's vaccine committee for use at 32 through 36 weeks of gestational age during RSV season. On August 24, 2023, ABRYSVO became the first and only RSV vaccine approved in the European Union (EU) for older adults and pregnant women. On January 26, 2024, the CDC issued a COCA Now email alert confirming that in most of the continental U.S., the RSV vaccine should be given to pregnant people from September through January 31 each year.

On April 1, 2025, Pfizer announced today that the European Commission (EC) has extended the indication to prevent LRTD caused by RSV in individuals 18 through 59. This expands the previous EC authorization for individuals aged 60 and older in Europe.

New York-based Pfizer Inc.'s (NYSE: PFE) portfolio includes medicines, vaccines, and many of the world's best-known consumer healthcare products. ABRYSVO™ trademark Application was filed on 2021-09-09.

ABRYSVO For Pregnant Women

On June 28, 2024, the U.S. CDC vaccine committee reviewed updated Abrysvo side effects when administered to pregnant women. In clinical trials among pregnant women at 24–36 weeks of gestation, more preterm births were noted among Pfizer RSV vaccine recipients compared to placebo recipients. The label for the Pfizer RSV vaccine notes the potential risk of preterm birth under the warnings and precautions section. 

On August 21, 2023, the U.S. FDA approved Abrysvo for use in pregnant individuals to prevent LRTD and severe LRTD caused by RSV in infants from birth through 6 months of age. Abrysvo is approved for use at 32 through 36 weeks of gestational age. The FDA reported the U.S. CDC Prescribing Information for Abrysvo includes a warning to inform that a numerical imbalance in preterm births in Abrysvo recipients (5.7%) occurred compared to those who received placebo (4.7%). The FDA says the available data cannot establish or exclude a causal relationship between preterm birth and Abrysvo. Two studies evaluated the safety of Abrysvo in pregnant women. In a clinical study among approximately 3,500 pregnant individuals who received Abrysvo, compared to approximately 3,500 pregnant individuals who received a placebo, Abrysvo reduced the risk of severe LRTD by 81.8% within 90 days after birth and 69.4% within 180 days after birth. Pfizer reported in August 2023 that ABRYSVO's potential risks include preterm birth.

ABRYSVO for Immunocompromised Adults

The first assessment from an RSV vaccine study in immunocompromised adults, conducted in August 2024, showed that ABRYSVO was well-tolerated and generated strong neutralizing responses after a single dose in adults aged 18 years and above. A single 120 µg dose of ABRYSVO elicited a strong neutralizing response against all RSV subtypes, including RSV-A and RSV-B, across all cohorts and age groups in the Phase 3 study. 

ABRYSVO Side Effects

The U.S. FDA required and approved safety labeling changes on January 7, 2025, to the Prescribing Information to include a new warning about the risk for Guillain-Barré syndrome (GBS). The U.S. CDC MMWR confirmed on May 30, 2024, that GBS was identified as a potential safety concern in clinical trials. Reports of GBS (5 per million doses of the Abrysvo vaccine administered) were more common than expected background rates.

ABRYSVO Coadministration

The U.S. CDC says available data on the immunogenicity of coadministration of RSV vaccines and other vaccines are currently limited says the U.S. CDC. Administering an RSV vaccine with one or more other vaccines at the same visit might increase local or systemic reactogenicity. The U.S. CDC approved ABRYSVO for coadministration with Dtap, influenza, and COVID-19 vaccines, but not smallpox or yellow fever. Pfizer reported on May 2, 2023, positive top-line results from the Phase 3 study evaluating the safety and immunogenicity of its RSV bivalent vaccine candidate, PF-06928316 or RSVpreF, coadministered with seasonal inactivated influenza vaccine in adults 65 years and older. The study met its primary endpoint, demonstrating noninferiority for all four flu strains and RSV groups. Pfizer's Briefing Document, presented on February 28, 2023, offered limited insights into the side effects or effectiveness of ABRYSVO when coadministered with influenza vaccines in Older Adults. ABRYSVO Pregnancy

The journal Clinical Infectious Diseases published a study in October 2023 titled "Safety and Immunogenicity of Bivalent RSVpreF Vaccine Coadministered with Seasonal Inactivated Influenza Vaccine in Older Adults" that concluded: The primary study objectives were met, demonstrating the noninferiority of RSVpreF and SIIV immune responses when RSVpreF was coadministered with SIIV and that RSVpreF had an acceptable safety and tolerability profile when coadministered with SIIV. The results of this study support the coadministration of RSVpreF and SIIV in an older adult population.

ABRYSVO Vaccine U.S. CDC Review

The U.S. Centers for Disease Control and Prevention (CDC) Advisory Committee on Immunization Practices (ACIP) conducted an ABRYSVO review on September 22, 2023, and February 23, 2023. The ACIP reviewed various presentations.

ABRYSVO Vaccine U.S. FDA Review

The U.S. Food and Drug Administration approved ABRYSVO™ for RSV prevention for Adults on October 23, 2024. The FDA conducted a Vaccines and Related Biological Products Advisory Committee (VRBPAC) ABRYSVO review on May 18, 2023. VRBPAC voted 14-0 regarding vaccine effectiveness in preventing severe disease in infants born to women vaccinated during pregnancy and voted 10-4 on immunization safety. In addition, the FDA's Briefing Document and Pfizer's EXECUTIVE SUMMARY were posted online. On February 28, 2023, the FDA conducted a VRBPAC meeting and published its Briefing Document, as did Pfizer. The VRBPAC voted that available data was adequate to support the safety and effectiveness of RSVpreF. The Committee voted 7 to 4 on safety and 7 to 4 on effectiveness. On February 21, 2023, the company announced the FDA had accepted for review a BLA for RSVpreF for the prevention of medically attended lower respiratory tract illness (MA-LRTI) and severe MA-LRTI caused by RSV in infants from birth up to six months of age by active immunization of pregnant individuals. The FDA has accepted the BLA for priority review and has set a PDUFA action date of August 2023. In addition, Pfizer confirmed on December 7, 2022, that the U.S. FDA accepted for priority review a Biologics License Application (STN 125769/0) for RSVpreF in individuals 60 years of age and older. In November 2018, the FDA granted Fast Track status to RSVpreF.

ABRYSVO Availability 2024

ABRYSVO's U.S. FDA approval(s) confirmed availability in late 2023. The European Medicines Agency (EMA) accepted Pfizer's ABRYSVO® marketing authorization application EMEA-002795-PIP01-20 under accelerated assessment for older adults and maternal immunization to help protect infants. On August 24, 2023, the EMA and European Commission issued approval. In February 2023, Pfizer Japan announced an application filed with the Ministry of Health, Labor, and Welfare for RSVPreF as a maternal immunization to help protect infants against RSV. In January 2023,  Health Canada approved  ABRYSVO.

ABRYSVO Safety Information

ABRYSVO should not be given to anyone with a history of a severe allergic reaction (e.g., anaphylaxis) to any of its components. Fainting can happen after injectable vaccines, including ABRYSVO. Precautions should be taken to prevent falls and injuries due to fainting. Adults with weakened immune systems, including those receiving medicines that suppress the immune system, may have a reduced immune response to ABRYSVO. In adults 60 years of age and older, the most common side effects (≥10%) were pain at the injection site, fatigue, headache, and muscle pain.

ABRYSVO Dosage

This vaccine is administered intramuscularly as a single dose of approximately 0.5 mL. A Phase III trial of a single 120 μg dose of RSVpreF, without aluminum hydroxide, is ongoing. The phase 2b study evaluated one of two dose levels of the vaccine, 120 or 240 μg, formulated with or without aluminum hydroxide.

ABRYSVO News

June 25, 2025 - Lower risk of dementia with AS01-adjuvanted vaccination against shingles and respiratory syncytial virus infections.

October 23, 2024 - Aamir Malik, Chief U.S. Commercial Officer and Executive Vice President, Pfizer, stated, “With this approval, we are proud that ABRYSVO is now the only RSV vaccine indicated for adults aged 18 to 49 at increased risk for the disease, expanding on its existing indications for older adults and pregnant women.”

Apr 8, 2024 - Pfizer Inc. announced Positive Top-Line results from a Phase 3 Study of ABRYSVO® in Adults Aged 18 to 59 at Increased Risk for RSV Disease.

January 4, 2023—Andréa Mueller, Primary Care Portfolio Lead at Pfizer Canada, commented, "For those eligible to receive the vaccine, getting vaccinated means helping to ensure babies are protected from their first breath and helping older adults continue doing what they love with a minimized risk of becoming infected. At Pfizer, we take pride in our decades of vaccine experience, helping to contribute positively to public health and the broader community."  

September 22, 2023 - Members of the Advisory Committee on Immunization Practices voted 11-1 to recommend the maternal RSV vaccine for pregnant women at 32 through 36 weeks gestation, using seasonal administration, to prevent RSV lower respiratory tract infection in infants.

February 28, 2023 - The U.S. FDA's VRBPAC voted (in favor of proceeding with ABRYSVO's BLA for older adults. Annaliesa Anderson, Ph.D., Senior Vice President and Chief Scientific Officer, Vaccine Research and Development, Pfizer, stated in a press release, "We are encouraged by the outcome of today's VRBPAC meeting as it is a testament to the strength of our science and dedication to bringing this important vaccine candidate to the market. We look forward to working with the FDA as it completes the review of our application."

November 1, 2022 - Pfizer announced the RSVpreF investigational vaccine was well-tolerated with no safety concerns for vaccinated individuals and their newborns. The results met one of the study protocol's pre-specified regulatory success criteria.

March 24, 2022 - The U.S. FDA awarded the RSVpreF vaccine candidate Breakthrough Designation.

June 22, 2020: Pfizer announces the start of Phase 3 clinical trials. One study (NCT04424316) of the RSV vaccine candidate, RSVpreF, in pregnant women will evaluate the safety and efficacy of RSVpreF compared to a placebo in infants born to immunized pregnant women.

May 22, 2018 - Pfizer Inc. announced that it had started a Phase 1/2 trial of its respiratory syncytial virus vaccine candidate in healthy adult volunteers. The highest risk of severe outcomes from RSV occurs in the first months of life.

RSVpreF RSV Clinical Trials

The RSV preF vaccine has been and is currently conducting several clinical trials.

On April 20, 2023, the NEJM published Original Articles: Bivalent Prefusion F Vaccine in Pregnancy to Prevent RSV Illness in Infants, and Efficacy and Safety of a Bivalent RSV Prefusion F Vaccine in Older Adults. CONCLUSIONS: RSVpreF vaccine prevented RSV-associated lower respiratory tract disease and RSV-associated acute respiratory illness in older adults (≥60 years of age) without evident safety concerns. 

ClinicalTrials.gov ID NCT05842967 - A Study to Assess the Safety, Tolerability, and Immunogenicity of RSVpreF in Adults at High Risk of Severe RSV Disease (MONET). Participants demonstrated RSV-A and RSV-B subgroup neutralizing responses non-inferior to the response seen in the Phase 3 RENOIR study of ABRYSVO in more than 34,000 adults aged 60 or older where vaccine efficacy was previously demonstrated. Participants also achieved a four-fold increase in serum neutralizing titers for RSV-A and RSV-B after receiving a receipt of ABRYSVO compared to those who had received it pre-vaccination. During the trial, ABRYSVO was well-tolerated, and safety findings were consistent with those from previous investigations of ABRYSVO in other populations.

RENOIR (NCT05035212) is a global, randomized, double-blind, placebo-controlled study designed to assess the efficacy, immunogenicity, and safety of a single dose of the vaccine in adults 60 years of age and older. The New England Journal of Medicine recently published the efficacy and safety results. RENOIR is ongoing, with efficacy data being collected in the second RSV season of the study.

MATISSE (NCT04424316) is a global, randomized, double-blinded, placebo-controlled Phase 3 study designed to evaluate the efficacy, safety, and immunogenicity of RSVpreF against medically attended lower respiratory tract illness (MA-LRT) and severe MA-LRTI due to RSV in infants born to healthy individuals vaccinated during pregnancy. The New England Journal of Medicine also recently published the efficacy and safety results.

On August 21, 2023, the FDA reported a clinical study that evaluated the effectiveness of Abrysvo in preventing LRTD and severe LRTD caused by RSV in infants born to individuals vaccinated during pregnancy. Among approximately 3,500 pregnant individuals who received Abrysvo, compared to about 3,500 pregnant individuals who received a placebo, Abrysvo reduced the risk of severe LRTD by 81.8% within 90 days after birth and 69.4% within 180 days after delivery. In a subgroup of pregnant individuals who were 32 through 36 weeks gestational age, of whom approximately 1,500 received Abrysvo and 1,500 received placebo, Abrysvo reduced the risk of LRTD by 34.7% and reduced the risk of severe LRTD by 91.1% within 90 days after birth when compared to placebo. Within 180 days after delivery, Abrysvo reduced the risk of LRTD by 57.3% and 76.5% for severe LRTD compared to placebo. The safety of Abrysvo was evaluated in two studies. In one study, approximately 3,600 pregnant individuals received a single dose of Abrysvo, and about 3,600 received a placebo. In the second study, about 100 pregnant individuals received Abrysvo, and approximately 100 received a placebo. The most commonly reported side effects by pregnant individuals who received Abrysvo were pain at the injection site, headache, muscle pain, and nausea.

In addition, although not commonly reported, a dangerous hypertensive disorder known as pre-eclampsia occurred in 1.8% of pregnant individuals who received Abrysvo compared to 1.4% of pregnant individuals who received a placebo. In the safety studies, infants' low birth weight and jaundice occurred more in the pregnant Abrysvo recipients than in pregnant placebo recipients.

The Phase 3 Study to Evaluate the Efficacy, Immunogenicity, and Safety of RSVpreF in Adults. (RENOIR), at the interim analysis (data-cutoff date, July 14, 2022), 34,284 participants had received the RSVpreF vaccine (17,215 participants) or placebo (17,069 participants). RSV-associated lower respiratory tract illness with at least two signs or symptoms occurred in 11 participants in the vaccine group (1.19 cases per 1000 person-years of observation) and 33 participants in the placebo group (3.58 points per 1000 person-years of observation) (vaccine efficacy, 66.7%; 96.66% confidence interval [CI], 28.8 to 85.8); 2 cases (0.22 cases per 1000 person-years of observation) and 14 cases (1.52 cases per 1000 person-years of observation), respectively, occurred with at least three signs or symptoms (vaccine efficacy, 85.7%; 96.66% CI, 32.0 to 98.7). RSV-associated acute respiratory illness occurred in 22 participants in the vaccine group (2.38 cases per 1000 person-years of observation) and 58 participants in the placebo group (6.30 cases per 1000 person-years of observation) (vaccine efficacy, 62.1%; 95% CI, 37.1 to 77.9). The incidence of local reactions was higher with the vaccine (12%) than with the placebo (7%); the incidences of systemic events were similar (27% and 26%, respectively). Similar rates of adverse events through 1 month after injection were reported (vaccine, 9.0%; placebo, 8.5%), with 1.4% and 1.0%, respectively, considered by the investigators to be injection-related. Severe or life-threatening adverse events were reported in 0.5% of vaccine recipients and 0.4% of placebo recipients. Serious adverse events were reported in 2.3% of participants in each group through the data-cutoff date.

Pfizer has initiated two additional clinical trials evaluating ABRYSVO. One trial is conducted in children at higher risk for RSV disease, ages 2-<18.8. A second trial is evaluating adults ages 18-60 at higher risk for RSV due to underlying medical conditions, such as asthma, diabetes, and COPD, and adults ages 18 and older who are immunocompromised and at high risk for RSV.8 Pfizer also plans postmarketing studies and surveillance programs to describe the safety of the vaccine further.

In a phase 2 efficacy study, Pfizer reported that the RSV vaccine showed 100% efficacy against mild to moderate RSV illness in adults (N=62). On June 24, 2022, the peer-reviewed journal NEJM published an original article based on the study's findings, which concluded that the RSVpreF vaccine was effective against symptomatic RSV infection and viral shedding. In addition, no evident safety concerns were identified.

In April 2020, a Phase 2b proof-of-concept study of RSVpreF achieved positive top-line results. This study evaluated the safety, tolerability, and immunogenicity of RSVpreF in vaccinated pregnant women ages 18 through 49 and their infants. Pfizer will publish outcomes from this clinical trial at a future date.

Beyfortus™ (Nirsevimab) RSV Monoclonal Antibody Clinical Trials, Dosage, Efficacy, Side Effects

Beyfortus™ (Nirsevimab-alip) (MEDI8897) is the first approved single-dose, extended half-life monoclonal antibody (mAb) offering passive immunization to prevent lower respiratory tract infections (LRTI) caused by the respiratory syncytial virus (RSV) in newborns and infants experiencing their first or second RSV season and those with congenital heart disease or chronic lung disease. Beyfortus binds to the prefusion conformation of the RSV fusion protein and was developed in partnership with AstraZeneca and Sanofi using AstraZeneca's technology. In clinical trials, Beyfortus was approximately 90% (95% CI, 75%-96%) protective against RSV-associated hospitalization in infants during their first RSV season.

The concept of using passive immunization strategies to prevent severe RSV illness during infancy is not new. The first proof-of-principle results were obtained from studies conducted in the mid-1980s using animal models of RSV infection. Palivizumab, a humanized RSV-F mouse monoclonal IgG1, was first approved by the U.S. Food and Drug Administration (FDA) in 1998. On July 17, 2023, the FDA Approved Beyfortus. As of May 2025, RSVVaxView reported that nirsevimab coverage among infants <8 months (born since April 1) ranged from 20.5% to 48.2%. Among U.S. territorial and affiliated island jurisdictions, coverage ranged from 0% to 47.8%.

The World Health Organization (WHO) published the preferred product characteristics of monoclonal antibodies for passive immunization against RSV  disease. In September 2024, the WHO SAGE recommended that all countries introduce passive vaccination to prevent severe RSV disease in young infants. In 2025, more than 25 countries are expected to offer Beyfortus. Beyfortus was approved by the European Union (EU) on November 4, 2022. Beyfortus was recommended in Australia, Canada, China, Europe  (EMEA/H/C/005304), Japan, and France. On July 25, 2024, the Ontario Ministry of Health announced a universal public program with Beyfortus. On May 29, 2025, data show that infant RSV hospitalizations in Spain decreased by 69% following immunization with BEYFORTUS, which targets infants only.

On May 8, 2025, the U.S. CDC MMWR reported a comparison of RSV-associated hospitalization rates among infants aged 0–7 months during 2024–25 with those during pre–pandemic RSV seasons, which were lower by an estimated 28% and 43%, respectively. On June 25, 2025, the CDC's ACIP reviewed a presentation titled "Effectiveness and Impact of RSV Prevention Products in Infants during the 2024–2025 RSV Season." On July 22, 2025, a study, published in PEDIATRICS®, an official journal of the American Academy of Pediatrics, met both of its co-primary endpoints, demonstrating that BEYFORTUS provides 87% reduction in cases of RSV disease across all sites of care among healthy, term babies, born ahead of or during the RSV season, and 98% reduction in hospitalizations of babies with RSV compared to those who did not get BEYFORTUS, per new post-hoc analysis.

Protein Chemical Formula: C6494H10060N1708O2050S46; Protein Average Weight: 146300.0 Da (approximate),  PubChem SID: 384585358, ChEMBL: ChEMBL4297575. CPT codes: 96380, 96381

In March 2017, Sanofi and AstraZeneca announced an agreement to develop and commercialize Beyfortus, with both companies sharing all costs and profits. Sanofi is listed on EURONEXT: SAN and NASDAQ: SNY. AstraZeneca (LSE/STO/Nasdaq: AZN) is a global, science-led biopharmaceutical company. BEYFORTUS - Trademark Details: 90557485. 

Beyfortus (Nirsevimab) Effectiveness

In November 2025, a study reported that the preventive effect of nirsevimab against RSV infection was observed not only for the first 6 months, but also potentially for up to 12 months after the last dose in children younger than 24 months. On May 29, 2025, Sanofi presented BEYFORTUS® public health advantage of BEYFORTUS®, bolstered by the first real-world comparison of infant vs maternal RSV immunization programs. It's the first real-world findings from the REACH public health impact study, along with updated findings from the HARMONIE Phase 3b clinical trial. REACH Public Health Impact Data: Late-breaking data from REACH show infant RSV hospitalizations were reduced by 69.0% in Spain following Beyfortus-only immunization targeted to all infants and 26.7% in the UK following RSVpreF-only maternal vaccination. The real-world results suggest substantial differences in the public health impact of the respective campaigns. HARMONIE Durability Data: New durability data from HARMONIE show Beyfortus sustained efficacy of 83% through six months, exceeding the typical length of the five-month RSV season. Half of infant RSV hospitalizations occur in babies born before the RSV season begins. These six-month results suggest that older babies can have season-long protection even if they are born and immunized with Beyfortus before the season starts.

In April 2025, a study concluded that the prophylactic administration of Nirsevimab after delivery significantly affects (reduces) the burden of severe acute viral bronchiolitis in pediatric intensive care, while substantially reducing the cost of care. In October 2024, The Lancet published a study (Volume 8, Issue 10) estimating effectiveness against RSV-associated hospitalizations for bronchiolitis at 73% (61–84), corresponding to one hospitalization averted for every 39 (26–54) doses administered. On July 10, 2024, the New England Journal of Medicine reported that in a real-world setting, Beyfortus reduced the risk of infant hospitalization for RSV-associated bronchiolitis by 83%. The effectiveness of therapy against RSV-associated bronchiolitis resulting in critical care was 69.6% (95% CI, 42.9 to 83.8) (27 of 193 case-patients [14.0%] vs. 47 of 146 matched control patients [32.2%]) and against RSV-associated bronchiolitis resulting in ventilatory support was 67.2% (95% CI, 38.6 to 82.5) (27 of 189 case-patients [14.3%] vs. 46 of 151 matched control patients [30.5%]).

On September 11, 2024, a study published by the American Academy of Pediatrics (AAP) concluded that Beyfortus (Nirsevimab) could effectively protect a broad infant population against RSV infection: 63.1% reduction in acute bronchiolitis-related hospital admissions (95% confidence interval [CI], 60.9% to 65.2%), and a 63.1% reduction in pediatric intensive care unit admissions (95% CI, 58.1% to 67.9%). As of September 28, 2024, the AAP recommends Beyfortus for all infants who are not otherwise protected through vaccination during pregnancy. On November 14, 2024, the CDC reported that in Alaska, nirsevimab was 89% effective in preventing RSV-associated hospitalization for infants in their first RSV season and 76% and 88% effective against medically attended illness for children in their first and second seasons, respectively. On November 26, 2024, a study published in The Pediatric Infectious Disease Journal concluded that in immunized infants, RSV-positive bronchiolitis was less frequent and less severe, with a significant reduction in hospitalization length compared to nonimmunized infants, resulting in substantial healthcare cost savings.

On April 29, 2025, a study concluded that the introduction of Nirsevimab was significantly associated with a reduction in hospitalizations and a decrease in the severity of RSV and other respiratory infections. Its use was associated with fewer admissions and a reduced need for intensive care, especially in infants infected with RSV, as well as in those infected with HMPV and adenovirus.

On June 28, 2024, the U.S. CDC vaccine committee reviewed presentations confirming the effectiveness of Beyfortus. On June 5, 2024, the journal Influenza and Other Respiratory Diseases published a Short Communication that estimated nirsevimab's effectiveness at 75.9% (48.5–88.7) in the primary analysis and 80.6% (61.6–90.3) and 80.4% (61.7–89.9) in two sensitivity analyses. During that 2023-2024 RSV season in the U.S., Beyfortus reduced RSV  hospitalizations by 82% (95% CI: 65.6 to 90.2) in infants under six months of age, compared to infants who received no RSV intervention, according to the interim results of an ongoing study published in The Lancet on April 30, 2024. 

Beyfortus (Nirsevimab) Availability

As of 2025, Beyfortus has protected infants in over 20 countries. Beyfortus will be available in the U.S. for the 2025-2026 RSV season in 50 and 100-mg injection doses. The CDC is releasing VFC Beyfortus throughout the RSV season, which is typically first detected in Florida.

In 2023-2024, 40.9% of infants received nirsevimab at a median age of 4 days, according to a study published in JAMA Network Open. Among 42 state and city IIS jurisdictions, the geographic coverage of nirsevimab among infants under 8 months ranged from 2.4% to 22.8% in 2024. Among eight U.S. territorial and affiliated island jurisdictions, coverage ranged from 0.0% to 14.9%.

Beyfortus (Nirsevimab) U.S. FDA

The U.S. FDA Approved Beyfortus in July 2023. The Vaccines and Related Biological Products Advisory Committee (VBPVAC) meeting on December 12, 2024, reviewed presentations on RSV immunization. The FDA's Antimicrobial Drugs Advisory Committee met on June 8, 2023, to discuss the Briefing Document and presentations (2) for the biologics license application (BLA) 761328 submitted by AstraZeneca AB for use with certain neonates, infants, and children. The Committee voted 21-0 in favor of approval. If approved by the FDA, nirsevimab could be available in the U.S. for the 2023/2024 RSV season. On February 5, 2019, the FDA granted Breakthrough Therapy Designation for MEDI8897, an extended half-life RSV F mAb, for the prevention of lower respiratory tract infections (LRTIs) caused by RSV.

Beyfortus (Nirsevimab) U.S. CDC

As of July 2024, the U.S. Centers for Disease Control and Prevention (CDC) recommends passive immunization to protect all infants under 8 months of age and some older babies at increased risk of severe RSV illness. The CDC Advisory Committee on Immunization Practices (ACIP) meeting on June 28, 2024, reviewed various presentations. On August 3, 2023, the ACIP reviewed recommendations, updated nirsevimab EtR, feasibility and implementation plans for monitoring safety and effectiveness in the second season, and Clinical considerations. The ACIP voted unanimously to include Beyfortus in the Vaccines for Children program and to use it in all infants under 8 months.

The CDC Morbidity and Mortality Weekly Report confirmed in March 2024 that the effectiveness was approximately 90% against RSV-associated hospitalizations in infants during their first RSV season. On January 4, 2024, the CDC advised healthcare providers to return to the recommendations (CDCHAN-00499) from the CDC and the Advisory Committee on Immunization Practices (ACIP) regarding the use of nirsevimab in young children. Infants and children who are recommended for nirsevimab should be immunized as soon as possible.

The ACIP previously met on June 22, 2023, and reviewed Clinical Considerations for RSVpreF maternal vaccine and nirsevimab, presented by Jefferson Jones, MD, MPH, FAAP. On February 23, 2023, the ACIP reviewed presentations on the following topics: Introduction, Cost-effectiveness analysis for nirsevimab – CDC model; Cost-effectiveness analysis for nirsevimab – Comparison to manufacturer model; Evidence to Recommendations framework for nirsevimab; Clinical considerations for nirsevimab; Safety and Efficacy of RSV Bivalent PreF Maternal Vaccine; and Workgroup considerations. On October 20, 2022, Dr. C. Felter presented the updated safety and efficacy of Nirsevimab to the ACIP. Previously, the ACIP meeting on June 23, 2022, reviewed Nirsavimab for The Prevention of RSV Disease in All Infants.

Beyfortus (Nirsevimab) Indication

In June 2021, the World Health Organization (WHO) published its preferred product characteristics for long-acting monoclonal antibodies (mAbs) for passive immunization against respiratory syncytial virus (RSV) disease in infants and children (as of June 2022). Nirsevimab is designed to be administered to infants born below eight months of age during the RSV season or children entering their first or second RSV season. Beyfortus is approved for use in infants who remain vulnerable to severe RSV disease through their second RSV season. RSV is a common, contagious virus that causes seasonal epidemics of LRTI, leading to bronchiolitis and pneumonia in infants. The Lancet published results from a study in February 2024 that concluded preterm infants accounted for about 25% of the RSV hospitalization burden in a meta-analysis. On October 26, 2023, the CDC hosted a COCA webinar, "Protecting Infants from RSV," which discussed the fact that approximately 2–3% of young infants are hospitalized for RSV. In Canada, the National Institute of Excellence in Health and Social Services recommends BEYFORTUS for the prevention of RSV LRTD in all neonates and infants aged 8 months or younger.   

Beyfortus (Nirsevimab) Dosage

Beyfortus is injected into the thigh muscle once. The recommended dose is 50 mg for children weighing less than 5 kg and 100 mg for children weighing 5 kg or more.

Beyfortus (Nirsevimab) Mechanism of Action

Nirsevimab is a recombinant human immunoglobulin G1 kappa (IgG1ĸ) long-acting mAb that binds to the prefusion conformation of the RSV F protein. RSV is coated with two types of glycoproteins: the attachment glycoprotein (G protein) and the fusion glycoprotein (F protein). Of these two, only the F protein is essential for the virus to enter cells lining the respiratory tract, making it a desirable target for drug development. The RSV F protein is initially in a metastable prefusion state and undergoes conformational changes upon triggering by an unknown event. These conformational changes lead to a postfusion conformation, in which both the viral and host-cell membranes are together. Nirsevimab binds to a highly conserved RSV prefusion F protein epitope, inhibiting the membrane fusion step in the viral entry process. This allows nirsevimab to neutralize various RSV A and B strains and block cell-to-cell fusion. Nirsevimab has also been modified with a triple amino acid substitution (M257Y/S259T/T261E [YTE]) in the Fc region to extend serum half-life from the typical 21–28 days to approximately 69 days.

Beyfortus (Nirsevimab) CPT Codes

As of October 6, 2023, the American Academy of Pediatrics (AAP) has approved two new Current Procedural Terminology (CPT) codes related to the administration of nirsevimab. One of these codes accounts for the work associated with providing counseling: 96380 Administration of RSV monoclonal antibody, seasonal dose, by intramuscular injection, with counseling by a physician or other qualified healthcare professional; and 96381 Administration of RSV monoclonal antibody, seasonal dose, by intramuscular injection.

Beyfortus Drug Safety-Related Labeling Changes

The price you pay for Beyfortus may depend on your child's dosage and whether you have health insurance. Severe hypersensitivity reactions (02/23/2024, SUPPL-7) have been reported following administration of BEYFORTUS. These reactions included urticaria, dyspnea, cyanosis, and/or hypotonia. Anaphylaxis has been observed with human immunoglobulin G1 monoclonal antibodies. If signs and symptoms of anaphylaxis or other clinically significant hypersensitivity reactions occur, initiate appropriate treatment.

Beyfortus Adverse Reactions Postmarketing Experience

Adverse reactions have been identified during the post-approval use of BEYFORTUS. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to estimate their frequency reliably or establish a causal relationship to drug exposure.

Sanofi SP0125

The Phase 3 clinical study evaluating the Sanofi SP0125 (VAD00001) live attenuated vaccine to prevent RSV in toddlers is expected to begin in 2024. SP0125 is administered through the nasal route.

Beyfortus (Nirsevimab) Price

Sanofi launched the BEYFORTUS Reservation Program, which provides critical insight into private healthcare provider demand and prioritizes fulfilling requests through the program. In Canada, each dose costs the province $1000.

On November 16, 2023, the CDC announced the release of Beyfortus to physicians and hospitals through the Federal Vaccines for Children Program and commercial channels. The Ordering Vaccines webpage provides additional guidance on ordering vaccines in the United States. On February 23, 2023, the U.S. CDC reviewed presentations: A cost-effectiveness analysis for nirsevimab—CDC model and a cost-effectiveness analysis for nirsevimab—Comparison to manufacturer model.

Beyfortus Sales

In April 2025, Sanofi announced that Beyfortus sales reached €284 million, driven by increased sales in the Northern Hemisphere, particularly in Germany and Japan. On January 30, 2025, Sanofi announced that Beyfortus sales were €841 million, driven by additional sales in Europe, Germany, and the U.S. The company announced on October 25, 2024, that during Q3, 15.7% sales growth was boosted by earlier-than-anticipated vaccine sales. Beyfortus sales totaled €645 million, driven by early delivery in the U.S. and the rollout in approximately 20 countries in 2024. Beyfortus sales totaled €18 million (USD 19.6 million) in the second quarter of 2024.

Beyfortus (Nirsevimab) News

July 22, 2025 - Ayman Chit, Head of North America Medical, Vaccines, Sanofi, stated in a press release, "These results support BEYFORTUS as a groundbreaking advancement in infant RSV disease prevention. With more than 40 real-world evidence studies to date, this latest study further strengthens the well-established body of data that shows that BEYFORTUS protects against RSV disease to help safeguard the health of all babies, regardless of whether they are born before or during the RSV season."

May 29, 2025 - Thomas Triomphe, Executive Vice President, Vaccines, Sanofi, stated: "The six-month data from HARMONIE show BEYFORTUS' protection exceeded the typical five-month RSV season. This is important because half of infant RSV hospitalizations occur in older babies born before the RSV season begins. These data demonstrating high, sustained efficacy, combined with real-world public health impact data, underscore how BEYFORTUS provides proven protection against the number one cause of lower respiratory tract disease in all infants."

December 9, 2024 - An Original Investigation: Respiratory Syncytial Virus Disease Burden and Nirsevimab Effectiveness in Young Children From 2023-2024 - nirsevimab was effective against RSV-associated hospitalization.

July 25, 2024—The Honourable Sylvia Jones, Ontario Deputy Premier and Minister of Health, commented, "Our government is taking steps to ensure Ontarians of all ages have the tools to be prepared and keep their loved ones safe and healthy before respiratory virus season. Our government is working with our partners to significantly expand Ontario's RSV program to make it easier for families to connect to the care they need, improve health outcomes, and reduce the number of hospitalizations and ICU admissions resulting from RSV."

June 28, 2024: The U.S. CDC vaccine committee reviewed various data presented by Amanda Payne, PhD, MPH, which support the continued use of Beyfortus for most infants during the 2024-2025 RSV season.

April 18, 2024—Delphine Lansac, General Manager of Vaccines Canada at Sanofi, said in a press release, "Parents and physicians who experience the impacts of RSV annually have been waiting for a preventative option that can cover the entire infant population and protect our most vulnerable.

January 2, 2024 - Professor Liu Hanmin, President of West China Second University Hospital, Sichuan University, commented in a press release, "There is currently no specific treatment for RSV disease in infants. This approval (Beyfortus) is crucial to preventing and controlling RSV disease in China."

December 14, 2023: The companies wrote, "We plan to provide approximately 230,000 additional doses—made up of 50mg and 100mg doses—for the U.S. in January. This would bring the first season's immunization rate to nearly 40 percent, significantly surpassing the prior pediatric immunization launch rates. A total of 1.4 million babies will be offered protection against RSV, a 27 percent increase over the initial supply forecast for the season.

August 3, 2023 - Thomas Triomphe, Executive Vice President of Vaccines, Sanofi, commented, "Today, we have turned the corner on the threat of RSV to our youngest, most vulnerable population. The ACIP's unanimous recommendations for the routine use of Beyfortus and its inclusion in the Vaccines for Children program are critical steps toward providing millions of parents in the U.S. with the ability to protect their babies through their first RSV season, when they are most susceptible to severe RSV disease. We appreciate the leadership of the FDA and CDC, as well as the ACIP public health experts, for recognizing and quickly acting on the threat that RSV poses to all infants. "May 12, 23—Thomas Triomphe, Executive Vice President of vaccine lines at Sanofi, stated, 'the HARMONIE data demonstrate the real-world impact  nirsevimab has on pediatric hospitalizations and illustrate its importance for infants, their families, and public health." November 4, 2022 - AstraZeneca and Sanofi announced that the European Commission had approved Beyfortus in the EU to prevent RSV lower respiratory tract disease in newborns and infants during their first RSV season.

May 11, 2022 - AstraZeneca announced results from a prespecified pooled analysis of the pivotal MELODY Phase III and Phase IIb trials showed AstraZeneca and SSanofi'snirsevimab demonstrated an efficacy (relative risk reduction versus placebo) of 79.5% (95% Confidence Interval [CI] 65.9 to 87.7; P<0.0001) against medically attended lower respiratory tract infections (LRTI), such as bronchiolitis or pneumonia, caused by RSV in infants born at term or preterm entering their first RSV season.

March 3, 2022 - Sanofi announced the New England Journal of Medicine published detailed results from a Phase 3 trial evaluating nirsevimab involving healthy infants born at term or late preterm (35 weeks gestational age or more significant) entering their first RSV season and met the primary endpoint, reducing the incidence of medically attended lower respiratory tract infections, such as bronchiolitis or pneumonia, caused by RSV by 74.5% (95% CI 49.6 to 87.1; P<0.001) compared to placebo.

August 11, 2021 - A peer-reviewed study concludes that, based on the mechanism of action of the new generation of antiviral mAbs, such as nirsevimab, which is highly specific in targeting viral antigenic sites, it is unlikely that it could interfere with the immune response to other vaccines.

March 3, 17—Sanofi Pasteur announced Today an agreement with the global biologics research and development arm of AstraZeneca to develop and commercialize MEDI8897, a monoclonal antibody 897, for the prevention of RSV-associated illness in newborns and infants. 

Beyfortus (Nirsevimab) Clinical Trials

Nirsevimab has been tested in several clinical trials. The primary endpoint (prevention of MA RSV was met in both trials: TI—Trial 03 RRR 70.1%, 95% CI (52.3%, 8, and 2%); TI—Trial 04 Primary Cohort RRR 74.9%, 95% CI (50.6%, 87.3%).

The JAMA Network published an Original Investigation on February 17, 2023, suggesting Beyfortus is associated with substantial benefits in preventing RSV infection in children. The peer-reviewed New England Journal of Medicine (NEJM) published a Correspondence on April 5, 2023, Nirsevimab for Prevention of RSV in Term and Late-Preterm Infants, and published a different Correspondence on March 3, 2022: Safety of Nirsevimab for RSV in Infants with Heart or Lung Disease or Prematurity. Found that at day 151, serum levels of nirsevimab were similar in the two cohorts and identical to those reported in the MELODY phase 2/3 clinical trial. The Phase 3 clinical study, Understanding Pre-Exposure Prophylaxis of NOVel Antibodies (SUPERNOVA), was last updated on April 3, 2023.

On May 12, 2023, Sanofi announced new data from the HARMONIE Phase 3b clinical trial show an 83.21% (95% CI 67.77 to 92.04; P<0.001) reduction in hospitalizations due to RSV-related LRTD in infants under 12 months of age who received a single dose of Beyfortus, compared to infants who received no RSV intervention. In addition, the data from HARMONIE also show that nirsevimab reduced the incidence of hospitalizations due to severe RSV-related LRTD (patients whose oxygen level is under 90% and require oxygen supplementation) by 75.71% (95% CI 32.75 to 92.91; P<0.001), and demonstrated a reduction of 58.04% in the incidence of all-cause LRTD hospitalization compared to infants who received no RSV intervention. On December 28, 2023, results (0.3% of those who received nirsevimab were hospitalized for RSV-associated lower respiratory tract infection compared with 1.5% of those who received standard care) from the HARMONIE clinical study indicated that Beyfortus protected infants against hospitalization for RSV-associated LRTD and against very severe RSV-associated lower respiratory tract infection in conditions that approximated real-world settings.

 In the MELODY and Phase 2b trials, the post-dose endpoint for Beyfortus was to reduce the incidence of medically attended lower respiratory tract infections (LRTIs) caused by RSV during the RSV season compared to placebo, achieved with a single dose. The Phase IIb study was a randomized, placebo-controlled trial designed to assess the efficacy of Beyfortus against medically attended lower respiratory tract infections (LRTIs) through post-dose. Healthy preterm infants of 29–35 weeks gestation were randomized (2:1) to receive a 50mg intramuscular injection of Beyfortus or a placebo. The dosing regimen was recommended following further analysis of the Phase IIb data. In the subsequent Phase III study, MELODY applied the recommended dosing regimen.

The MELODY Phase III study was a randomized, placebo-controlled trial conducted in 21 countries. Its purpose was to determine the efficacy of Beyfortus against medically attended lower respiratory tract infections (LRTIs) due to respiratory syncytial virus (RSV), as confirmed by reverse transcriptase polymerase chain reaction testing 150 days after dosing, versus placebo in healthy late preterm and term infants (35 weeks' gestational age or more) entering their first RSV season.

MEDLEY was a Phase II/III, randomized, double-blind, Synagis-controlled trial to assess safety and tolerability for Beyfortus in preterm infants and infants with congenital heart disease and/or chronic lung disease of prematurity (CLD) eligible to receive Synpost-dose9 Between July 2019 and May 2021, approximately 918 infants entering their first RSV season were randomized to receive a single 50mg (in infants weighing <5kg) or 100mg (in infants weighing ≥5kg) intramuscular injection of Beyfortus or Synagis. Safety was assessed by monitoring the occurrence of TEAEs and TESAEs through post-dose. Serum levels of Beyfortus following dosing (on day 151) in this trial were comparable to those observed in the MELODY Phase III trial, indicating similar protection in this population to that in healthy term and late preterm infants is likely. The data was published in the New England Journal of Medicine in March 2022.