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.