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Typbar TCV® Typhoid Vaccine

Bharat Biotech International's Typbar TCV® is a vaccine containing a polysaccharide of Salmonella typhi Ty2 conjugated to Tetanus Toxoid. A human challenge study at the University of Oxford demonstrated that the vaccine is safe, 100% immunogenic, and prevents up to 87.1% of infections when using real-life definitions of typhoid fever. Vi Capsular polysaccharide of Salmonella typhi alone elicits B cell responses. In addition, the conjugation of bacterial polysaccharides to a protein carrier provides foreign peptide antigens presented to the immune system, eliciting antigen-specific CD4+ Th cells, referred to as T-dependent antibody responses. A hallmark of T-dependent responses elicited by toxoids is to induce higher-affinity antibodies and long-term immune memory.

A human challenge study at the University of Oxford demonstrated that the vaccine is safe, immunogenic, and prevents up to 87.1% of infections using real-life definitions of typhoid fever. A mathematical modeling study supported by Gavi published on February 3, 2022 - Estimating the effect of vaccination on antimicrobial-resistant typhoid fever in 73 countries - found the introduction of routine immunization with TCV at age nine months with a catch-up campaign up to age 15 years was predicted to avert 46–74% of all typhoid fever cases.

The peer-reviewed journal The Lancet published an early-release (September 1, 2022) phase 3 study funded by the Gates Foundation - Safety and immunogenicity of a typhoid conjugate vaccine among children aged nine months to 12 years in Malawi: a nested substudy of a double-blind, randomized controlled trial. This study provides evidence of TCV vaccination safety, tolerability, and immunogenicity up to 730–1,035 days in Malawian children aged nine months to 12 years. On January 25, 2024, updated results from the phase 3 clinical study were published today in The Lancet. The research team enrolled more than 28,000 healthy children in Malawi. It randomly assigned about half the group to receive the TCV and the other half to receive a meningococcal capsular group A conjugate (MenA) control vaccine. During the more than four years of follow-up, 24 children in the TCV group and 110 in the MenA group developed typhoid fever, which was confirmed via blood culture. That resulted in an efficacy of 78.3 percent in the TCV group, with one case of Typhoid prevented for every 163 children vaccinated. TCV was effective in all age groups, and over the study period – which ended in 2022 – vaccine efficacy remained strong, decreasing by only 1.3 percent per year.

Typbar TCV is the only U.S. FDA-approved vaccine for children less than two years of age. Typhoid fever caused by multidrug-resistant H58 Salmonella Typhi is an increasing public health threat in sub-Saharan Africa. In addition, Typbar TCV has been recommended by the experts at the WHO-Strategic Advisory Group for routine immunizations and is WHO-prequalified.

Bharat Biotech is a pioneering biotechnology company known for its world-class R&D and manufacturing capabilities. The Bill & Melinda Gates Foundation funds TyVAC.

Typbar TCV Indication

Vaccination can help prevent typhoid fever, an acute enteric disease caused by Salmonella enterica serovar Typhi (S Typhi). S Typhi is a rod-shaped, gram-negative, anaerobic bacterium expressing surface polysaccharide capsule (Vi antigen), a critical virulence determinant. The UU.S.CDC recommends vaccination for people traveling to places with common typhoid fever, says the UU.S.CDC. Typhoid fever remains a significant cause of morbidity and mortality in low-income and middle-income countries, says the WHO. Typhoid fever, a systemic febrile illness caused by Salmonella enterica serovar Typhi, is responsible for more than 9 million infections and more than 110,000 deaths globally annually. The highest disease burden was observed among children.

The Typbar TCV vaccine is indicated as a preventative vaccine against Typhoid, which Salmonella Typhi and Paratyphi cause. If it is not treated, it can kill up to 30% of people who get it. Some people who get Typhoid become "carriers," who can spread the disease to others. Curbing typhoid transmission can also prevent resistant plasmid transfer to other bacterial pathogens. Our results can help inform country-level decision-making and prioritize TCV introduction in countries with a high incidence of antimicrobial-resistant typhoid fever.

Typbar TCV Dosage

The WHO recently recommended that routine childhood immunization programs include Typbar TCV as a single intramuscular dose for primary vaccination of infants and children from 6 months of age. It is also recommended for adults ≤45 years of age and in catch-up campaigns in typhoid-endemic regions in children ≤15 years of age.

According to the U.S., two typhoid fever vaccines are available in the USA. However, typhoid vaccines are not 100% effective. Oral vaccine: Can be given to people at least six years old. It consists of four pills taken every other day and should be finished at least one week before travel. An injectable vaccine that can be given to people at least two years old should be given at least two weeks before travel.

The Typbar-TCV is a WHO-prequalified tetanus-toxoid conjugated Vi-TCV containing 25 μg of Vi polysaccharide per 0.5-ml dose. 

Typbar TCV News

January 25, 2024 - "The newly published study supports the long-lasting impacts of a single shot of TCV, even in the youngest children, and offers hope of preventing typhoid in the most vulnerable children," said Kathleen Neuzil, MD, MPH.

August 10, 2022 - A new study finds the Typbar TCV® vaccine provides immunity for up to three years in children as young as nine months old and is safe and well tolerated. INotably, the vaccine can be given to nine-month-old infants at the same time as routine measles-rubella vaccinations without reducing the immune response to either vaccine.

June 21, 2022 - The Lancet Microbe reported while multi-drug resistance to first-line antibiotics has generally declined in South Asia, strains resistant to macrolides and quinolones – two of the most important antibiotics for human health – have risen sharply and spread frequently to other countries.

April 7, 2022 - With support from Gavi, the Vaccine Alliance, WHO, UNICEF, and other partners, the Government of Nepal today launched a new vaccine campaign introducing Typhoid Conjugate Vaccine into the routine immunization program. The campaign aims to reach 95% coverage of nearly 7.5 million children.

February 3, 2022 - A meta-analysis of disease burdens in 73 countries eligible for support from Gavi, Birger, and colleagues has shown that the introduction of routine immunization of children from age nine months with typhoid conjugate vaccines, with a catch-up program up to age 15 years, would avert about 66 million cases and 826,000 deaths caused by typhoid fever over ten years. 

November 1, 2021 - The Lancet Global Health published the final results of the Phase 3 clinical trial. These results are from the 2-year follow-up of 20,019 children aged nine months to < 16 years of age. The final results are similar to the interim results. There is no evidence of waning protection over the two years. These results support the WHO recommendations to vaccinate children in endemic typhoid settings. 

September 16, 2021 - The New England Journal of Medicine published a study that found a single dose of Typhoid conjugate vaccine is safe and 84 percent effective in protecting against Typhoid in Blantyre, Malawi. An intention-to-treat analysis comparing this incidence with that in the Vi-TCV group yielded a protective efficacy of Vi-TCV of 80.7%. The effectiveness of Vi-TCV was similar in children younger than five years of age and children who were five years of age or older at the time of vaccination, and this efficacy remained consistent throughout the observation period.

August 21, 2021 - Recent data confirmed Bangladesh has one of the highest typhoid burdens in the world. A study conducted in Mirpur, Dhaka, with typhoid conjugate vaccine (TCV), has found that the vaccine prevents 85% of cases among vaccinated children aged nine months to 15 years.

August 9, 2021 - A new study conducted in Mirpur, Dhaka, with typhoid conjugate vaccine (TCV) and published by The Lancet found that the vaccine prevents 85% of cases among vaccinated children aged nine months to 15 years.

July 1, 2021 - UNICEF, Gavi, the Vaccine Alliance, and the WHO have partnered with the Ministry of Health and Child Care to launch a new vaccine campaign introducing TCV into the routine immunization schedule across Zimbabwe, which is the third country in the world to introduce the typhoid conjugate vaccine into the regular immunization program showing Zimbabwe's leadership in immunization in the Africa region and globally. In 2019, Pakistan introduced the vaccine into routine immunization schedules, and Liberia followed suit in April 2021.

April 5, 2021 - Liberia became the first country in Africa to introduce the typhoid conjugate vaccine (TCV) with a weeklong campaign to reach more than 1.9 million children aged nine months to younger than 15 years old with TCV. After the campaign concludes, TCV will become a routine immunization for all children at nine months old.

February 12, 2021 - U.S. reports extensive drug-resistant salmonella typhi infections among residents without international travel.

February 1, 2021 - The next step: Lifesaving typhoid conjugate vaccines reach Punjab province, Pakistan. For the next two weeks, vaccination teams will be in Islamabad and 12 districts of Punjab province to vaccinate nearly 12.7 million children between 9 months to 15 years against Typhoid. Keeping children protected against typhoid diseases, we help keep children in school and spare families the economic hardship of typhoid diagnosis and treatment. 

January 4, 2021- How a scientist's return kickstarted Bharat Biotech's journey. The company also developed and launched Typbar TCV, the world's first clinically proven and WHO-prequalified TCV, which can be administered to even a six-month-old.

September 30, 2020 - Travel Alert: EExtensive drug-resistant typhoid fever in Pakistan. The CDC recommends that all travelers (even short-term travelers) to South Asia, including Pakistan, be vaccinated against typhoid fever before travel.

November 18, 2019 - Pakistan became the first to introduce TCV into the routine immunization system, and the world watched. Nearly 10 million children were vaccinated in just three weeks in Sindh province, protecting them against a potentially deadly disease and sparing their families the economic hardship that so often comes with a case of Typhoid.

January 3, 2018 - Typbar TCV from Bharat Biotech, World's First Typhoid Conjugate Vaccine Prequalified by WHO. This enables the procurement and supply of this lifesaving vaccine to UNICEF, Pan-American Health Organization, and GAVI-supported countries. In addition, Typbar TCV® has been evaluated in Human Challenge Studies at Oxford University, and typhoid conjugate vaccines have been recommended by WHO's Strategic Advisory Group of Experts on Immunization.

Typbar TCV Typhoid Vaccine Clinical Trials

Clinical Trial NCT03299426: Among Malawian children nine months to 12 years of age, administration of Vi-TCV resulted in a lower incidence of blood culture-confirmed typhoid fever than the MenA vaccine. Last updated on 2023-02-08.

Clinical Trial NCT03933098: Immune Non-inferiority and Safety of a Vi-DT Typhoid Conjugate Vaccine. This is a multicenter, observer-blinded, randomized, active-controlled, Phase 3 study in healthy Nepalese aged six months to 45 years at the first vaccine dose.

Clinical Trial NCT03600025:  Cellular Immune Responses in Typhoid Fever Patients and Vaccinees (Recruiting). This Phase 1 clinical trial aims to understand further the role of mucosal-associated invariant T cell (MAIT) and natural killer (NN.K. cell responses in typhoid fever or following vaccination.

INO-4500 DNA Vaccine Description 2022

INO-4500 is a DNA vaccine candidate. On November 17, 2022, the company discontinued the development of product candidates targeting Lassa Fever (INO-4500) following initial analyses of data from studies conducted by INOVIO and funded by CEPI.

In addition, INOVIO is leveraging its optimized plasmid design and delivery technology to develop DNA medicines to treat and prevent infectious diseases. INO-4500 is the first vaccine candidate for Lassa fever to enter human trials, says the company.

INOVIO's DNA medicines deliver optimized plasmids directly into cells intramuscularly or intradermally using one of INOVIO's proprietary hand-held CELLECTRA smart devices. INOVIO's DNA medicines are made using a process called SynCon®. SynCon uses a proprietary computer algorithm designed to identify and optimize the DNA sequence of the target antigen, whether it is a virus or a tumor. Once this sequence has been determined, the DNA is synthesized or reorganized, and manufacturing can begin, says the company.

DNA medicines are composed of optimized DNA plasmids, which are small circles of double-stranded DNA synthesized or reorganized by computer sequencing technology and designed to produce a specific immune response in the body.

On February 23, 2021, INOVIO announced the first participant was dosed in a Phase 1B clinical trial for INO-4500 in Ghana, Africa. The Phase 1B clinical trial (LSV-002) is ongoing at the Noguchi Memorial Institute for Medical Research in Accra, Ghana. It is the first vaccine clinical trial for Lassa fever to be conducted in West Africa.

Plymouth Meeting, Pennsylvania-based INOVIO is a biotechnology company focused on rapidly bringing to market precisely designed DNA medicines to treat and protect people from infectious diseases, cancer, and diseases INOVIO has 15 DNA medicine clinical programs currently in development focused on HPV-associated diseases, cancer, and infectious diseases, including coronaviruses associated with MERS and COVID-19 diseases being developed under grants from the Coalition for Epidemic Preparedness Innovations and the U.S. Department of Defense.

INO-4500 Indication

The U.S. CDC says Lassa fever is an animal-borne, or zoonotic, acute viral illness. It is endemic in West Africa, including Sierra Leone, Liberia, Guinea, and Nigeria. Neighboring countries are also at risk, as the animal vector for the Lassa virus, the "multimammate rat" (Mastomys natalensis), is distributed throughout the region.

The illness was discovered in 1969 and is named after the town in Nigeria where the first cases occurred. An estimated 100,000 to 300,000 infections of Lassa fever occur annually, with approximately 5,000 deaths, says the CDC. Unfortunately, surveillance for Lassa fever is not standardized; therefore, these estimates are crude. However, in some areas of Sierra Leone and Liberia, it is known that 10-16% of people admitted to hospitals annually have Lassa fever, demonstrating the serious impact the disease has on the region.

INO-4500 Dosage

The INO-4500 vaccine is conducting clinical tests for the prevention of Lassa Fever. Inovio's proprietary Cellectra electroporation device injects this vaccine into the muscle or skin. Injection of the DNA plasmid into a patient generates robust in vivo monoclonal antibody production. Thus, this approach can potentially generate in vivo production of therapeutic antibodies.

INOVIO's Phase 1B clinical trial, LSV-002, dosing regimen involves two vaccinations at 0 and 28 days with either 1.0 mg or 2.0 mg dosing levels. This trial will inform dose selection for subsequent Phase 2 studies in West Africa.

INO-4500 News 2018 - 2022

March 22, 2022 - The UK NHS confirmed a systematic review examining preclinical and human pharmacokinetic data and found that the clinical evidence for ribavirin as a treatment for Lassa fever was limited. 

March 15, 2022 - The U.S. CC confirmed an outbreak of Lassa fever in Nigeria in Ondo, Edo, Bauchi, Ebonyi, Kogi, Taraba, Enugu, Benue, Gombe, Nasarawa, and the Delta States.

February 21, 2022 - The WHO stated 'Considering the seasonal increases of cases between December and March, countries in West Africa that have endemic Lassa fever are encouraged to strengthen their related surveillance systems to enhance early detection and treatment of cases and to reduce the case fatality rate, as well as to strengthen cross border collaboration.'

February 9, 2022 - The UK Health Security Agency press office confirmed two people had been diagnosed with Lassa fever in the East of England. Before these cases, 8 cases of Lassa fever were imported to the UK since 1980. The last 2 cases occurred in 2009. There was no evidence of onward transmission from any of these cases.

November 7, 2021 - The WHO Africa reported through October 2021 that Nigeria had confirmed 403 cases. A total of 79 individuals have died among those who had confirmed results, yielding a 19.6% CFR this year. The CFR during the same period in 2020 was 20.7%

October 26, 2021 - INOVIO announced its Phase 1B clinical trial for INO-4500, its DNA vaccine candidate for Lassa fever, and completed full enrollment of 220 participants. This trial is ongoing at the Noguchi Memorial Institute for Medical Research in Accra, Ghana. It is the first vaccine clinical trial for Lassa fever conducted in West Africa, where the viral illness is endemic.

February 23, 2021 - INOVIO announced the first participant was dosed in a Phase 1B clinical trial for INO-4500, its DNA vaccine candidate for Lassa fever, in Ghana. The Phase 1B clinical trial (LSV-002), ongoing at the Noguchi Memorial Institute for Medical Research in Accra, Ghana, is the first vaccine clinical trial for Lassa fever to be conducted in West Africa, where the infection is endemic.

October 11, 2018 - According to new research published in Nature Communications, a novel vaccine designed to protect people from Lassa fever and rabies showed promise in preclinical testing. The investigational vaccine, called LASSARAB, was developed and tested by scientists at Thomas Jefferson University in Philadelphia; the University of Minho in Braga, Portugal; the University of California, San Diego; and the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health.

April 11, 2018 -  Inovio Pharmaceuticals, Inc. (NASDAQ: INO) and the Coalition for Epidemic Preparedness Innovations announced a partnership under which Inovio will develop vaccine candidates against Lassa fever and Middle East Respiratory Syndrome.

INO-4500 Clinical Trials 

Clinical Trial NCT04093076: INOVIO's Phase 1B clinical trial, LSV-002, will enroll approximately 220 adult participants 18-50 years old, with the primary endpoint of evaluating safety and immunogenicity in an African population. The dosing regimen involves two vaccinations at 0 and 28 days with either 1.0 or 2.0 mg dosing levels. In addition to providing valuable insights on the INO-4500 safety and immunogenicity profile, this trial will inform dose selection for subsequent Phase 2 studies in West Africa. Last Update Posted: February 25, 2021. Estimated study completion date: September 2022.

Clinical Trial NCT03805984:  Safety, Tolerability, and Immunogenicity of INO-4500 in Healthy Volunteers. This Phase 1 trial is a randomized, double-blinded, placebo-controlled, placebo-controlled trial to evaluate the safety, tolerability, and immunological profile of INO-4500 administered by intradermal (ID) injection followed by electroporation using the CELLECTRA® 2000 device in healthy adult volunteers. Last Update Posted: November 23, 2020. Actual completion date: October 21, 2020.

VAXNEUVANCE™ Pneumococcal Vaccine Clinical Trials, Dosage, Indication, News, Side Effects

The U.S. Food and Drug Administration (FDA) approved Merck's VAXNEUVANCE™ on July 16, 2021, for active immunization for the prevention of invasive pneumococcal disease (IPD) caused by 15 serotypes conjugated to a CRM197 carrier protein, including Streptococcus pneumoniae serotypes 1, 3, 4, 5, 6A, 6B, 7F, 9V, 14, 18C, 19A, 19F, 22F, 23F, and 33F, in adults. On June 22, 2022, the FDA approved (STN: 125741) an expanded indication for VAXNEUVANCE, which now includes children aged six weeks through 17 years. The FDA published a Package Insert, Patient Information sheet, and BLA Clinical Review Memorandum; STN: 125741.

On January 28, 2022, the U.S. CDC confirmed that using PCV20 alone or PCV15 in combination with PPSV23 is expected to reduce pneumococcal disease incidence in adults aged 65 years and older, as well as in those aged 19–64 years with certain underlying conditions. Natalie Banniettis, MD, FAAP, Senior Principal Scientist, Global Clinical Development, Merck Research Laboratories, Merck & Co., presented (V114, VAXNEUVANCE): Pediatric Clinical Development Program on February 24, 2022. Merck states that vaccinating with VAXNEUVANCE pneumococcal polysaccharides may not protect all vaccine recipients.

On December 15, 2021, the European Commission approved VAXNEUVANCE EMEA/H/C/005477 for use by adults. On October 24, 2022, the European Commission approved the expanded approval for infants, children, and adolescents aged 6 weeks to less than 18 years.

For more information on the VAXNEUVANCE vaccine, visit www.merck.com or this Merck webpage. The brand is trademarked in Canada. ATC code: J07AL02. U.S. Patent No. 8,192,746. 

VAXNEUVANCE Vaccine Revenues

On April 26, 2025, Merck announced that Vaxneuvance produced $230 million in revenues. Growth was primarily driven by higher demand in the Europe and Asia Pacific regions, partially offset by lower demand in the U.S. due to competitive pressure. On April 25, 2024, Merck announced that Vaxneuvance generated $219 million in revenues during the first quarter of 2024, representing a 106% increase from the prior year period. 

VAXNEUVANCE Vaccine Indication

VAXNEUVANCE is indicated for active immunization to prevent invasive disease caused by the S. pneumoniae serotypes contained in the vaccine in adults. According to the U.S. FDA disclosure, more than 90 types of pneumococcal bacteria can affect adults differently than children. Pneumococcal serotypes not in the currently licensed conjugate vaccine, such as 22F and 33F, are commonly associated with invasive pneumococcal disease. For example, serotypes 22F and 33F now account for 13% of the invasive pneumococcal disease seen among adults aged 65 and older in the U.S. and 7-12% of European adult cases.

Additionally, serotype 3 remains one of the leading causes of invasive pneumococcal disease in adults and children, despite being included in currently available pneumococcal vaccines. For example, in the U.S., the U.S. CDC says that 15% of invasive pneumococcal disease among adults aged 65 and older continues to be caused by serotype 3. And this ranges from 12 to 18% of adult cases across European countries.

Children under the age of 2 are particularly vulnerable to pneumococcal infection, and the incidence of invasive pneumococcal disease remains highest in the first year of life. There are 100 different types of pneumococcal bacteria, including serotypes 22F, 33F, and 3, which collectively represent more than a quarter of invasive pneumococcal disease cases in children under 5.

The U.S. CDC Advisory Committee on Immunization Practices (ACIP) met on October 20, 2021, and unanimously voted to update pneumococcal vaccination recommendations for adults 65 and older and those ages 19 to 64 with certain underlying medical conditions or other disease risk factors. In both groups, the ACIP voted to recommend vaccination with a sequential regimen of VAXNEUVANCE followed by PNEUMOVAX 23 or with a single dose of 20-valent pneumococcal conjugate vaccine. These updates would apply to adults who have not received a pneumococcal conjugate vaccine or whose previous pneumococcal vaccination history is unknown.

VAXNEUVANCE Dosage

Merck's VAXNEUVANCE is administered as an intramuscular injection. When PCV15 is used, the CDC recommends a minimum of one year between the administration of PCV15 and PPSV23. A minimum interval of 8 weeks can be considered for adults with an immunocompromising condition, a cochlear implant, or a cerebrospinal fluid leak to minimize the risk of IPD caused by serotypes unique to PPSV23 in these vulnerable groups. Adults who have only received PPSV23 may receive a PCV (either PCV20 or PCV15) ≥ one year after their last PPSV23 dose. When PCV15 is used in individuals with a history of receiving PPSV23, it must be followed by another dose of PPSV23.

VAXNEUVANCE Coadministration

The CDC confirmed PCV15, PCV20, or PPSV23 could be coadministered with QIV in an adult immunization program as concomitant administration (PCV15 or PPSV23 and QIV [Fluarix], PCV20, and adjuvanted QIV [Fluad]) has been demonstrated to be immunogenic and safe. However, slightly lower pneumococcal serotype-specific OPA GMTs or geometric mean concentrations were reported when pneumococcal vaccines were coadministered with QIV than when pneumococcal vaccines were given alone. Currently, there is no data on the coadministration of this vaccine with other vaccines (e.g., tetanus, diphtheria, acellular pertussis vaccine, hepatitis B, or zoster vaccine) among adults. Evaluation of coadministration of PCV15, PCV20, or PPSV23 with COVID-19 vaccines is ongoing.

VAXNEUVANCE Side Effects

Do not administer VAXNEUVANCE to individuals with a severe allergic reaction to any VAXNEUVANCE or diphtheria toxoid component. Additionally, individuals with altered immunocompetence, including those receiving immunosuppressive therapy, may have a reduced immune response to VAXNEUVANCE. The most commonly reported solicited adverse reactions in individuals 18 through 49 years of age were injection site pain (75.8%), fatigue (34.3%), myalgia (28.8%), headache (26.5%), injection site swelling (21.7%), injection site erythema (15.1%) and arthralgia (12.7%). The most commonly reported solicited adverse reactions in individuals 50 years of age and older were injection site pain (66.8%), myalgia (26.9%), fatigue (21.5%), headache (18.9%), injection site swelling (15.4%), injection site erythema (10.9%) and arthralgia (7.7%).

VAERS is a U.S. passive reporting system, meaning it relies on individuals to send in reports of their experiences with a vaccine. However, anyone, including parents and patients, can submit information to VAERS. Furthermore, healthcare providers are required by law to report to VAERS. People are also encouraged to report the adverse side effects of prescription drugs to the FDA. Visit www.fda.gov/medwatch or call 1–800–FDA–1088.

VAXNEUVANCE Availability

As of 2024, VAXNEUVANCE was available in the U.S., the U.K., and Europe. On April 27, 2023, Merck reported higher sales of VAXNEUVANCE, which increased to $106 million, primarily due to continued uptake in the pediatric indication following its launch in the U.S. 

VAXNEUVANCE News

June 13, 2023 - VAXNEUVANCE (V114) was found to be well-tolerated and safe for infants, according to a study published in the journal Pediatrics.

October 24, 2022 - Dr. Eliav Barr, SVP, head of global clinical development and chief medical officer, Merck Research Laboratories, stated in a press release: "With this (EC) approval, we are pleased to bring an important new PCV option to a vulnerable population in Europe, including infants less than one year of age, who typically experience the highest rates of disease."

September 16, 2022 - Dr. Eliav Barr, senior vice president, head of global clinical development, and chief medical officer, Merck Research Laboratories, stated, "We are pleased with the CHMP's positive opinion as it brings us one step closer to our goal of helping to protect against pneumococcal strains that pose a substantial risk to infants and children in Europe."

July 28, 2022 - The U.S. CDC's ACIP unanimously voted to provisionally recommend using VAXNEUVANCE as an option to the currently available 13-valent pneumococcal conjugate vaccine (PCV13) for children under 19 years according to the presently recommended PCV13 dosing and schedules.

December 15, 2021 - Merck announced today that the European Commission has approved VAXNEUVANCE for active immunization to prevent invasive disease and pneumonia caused by Streptococcus pneumoniae in individuals 18 years of age and older. The approval enables the marketing of VAXNEUVANCE in all 27 member states of the European Union, as well as in Iceland, Norway, and Liechtenstein.

December 1, 2—Merck announced that the U.S. FDA has accepted for Priority Review a supplemental Biologics License Application for VAXNEUVANCE to prevent invasive pneumococcal disease in children six weeks through 17 years of age. Additionally, the FDA has set a target action date under the Prescription Drug User Fee Act of April 1, 2022.

October 20, 2021 - Merck announced the U.S. Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices (ACIP) unanimously voted in favor of updates to pneumococcal vaccination recommendations for adults 65 years and older and adults ages 19 to 64 with certain underlying medical conditions (e.g., chronic conditions such as diabetes, chronic heart disease, chronic lung disease, or chronic liver disease, as well as HIV) or other disease risk factors (e.g., smoking, alcoholism). In both groups, the ACIP voted to provisionally recommend vaccination with either a sequential regimen of VAXNEUVANCE followed by PNEUMOVAX23 or a single dose of 20-valent pneumococcal conjugate vaccine. These updates would apply to adults who have not received a pneumococcal conjugate vaccine or whose previous pneumococcal vaccination history is unknown.

October 15, 2021 - Merck announced that the European Medicines Agency's Committee for Medicinal Products for Human Use (CHMP) had recommended the approval of VAXNEUVANCE™.

August 25, 2021 - Merck announced topline results from the pivotal PNEU-PED (V114-029) study evaluating the immunogenicity, safety, and tolerability of VAXNEUVANCE™ in 1,720 healthy infants enrolled between 42-90 days of age. In the PNEU-PED study, primary endpoints demonstrated that VAXNEUVANCE had a safety profile generally comparable to PCV13 following receipt of any vaccine dose. Secondary endpoints demonstrated statistically superior immune responses for VAXNEUVANCE compared to PCV13 for shared serotypes three and unique serotypes 22F and 33F, based on prespecified criteria. Additionally, VAXNEUVANCE showed non-inferior immune responses to antigens contained in several routinely used pediatric vaccines when administered concomitantly with VAXNEUVANCE or PCV13.

July 16, 2021 - Merck today announced the U.S. Food and Drug Administration approved VAXNEUVANCE™ (Pneumococcal 15-valent Conjugate Vaccine) (pronounced VAKS-noo-vans) for active immunization for the prevention of invasive disease caused by Streptococcus pneumoniae serotypes 1, 3, 4, 5, 6A, 6B, 7F, 9V, 14, 18C, 19A, 19F, 22F, 23F and 33F in adults 18 years of age and older.

May 20, 2021 - Merck announced that V114, the company's investigational 15-valent pneumococcal conjugate vaccine, met its primary immunogenicity and safety endpoints in the V114 Phase 3 pediatric clinical program.

January 12, 2—Merck announced that the U.S. FDA accepted for priority review a Biologics License Application (BLA) for V114, Merck's investigational 15-valent pneumococcal conjugate vaccine, for the prevention of invasive pneumococcal disease in adults 18 years of age and older. Additionally, the FDA established a target action date under the Prescription Drug User Fee Act, as of July 18, 2021. The European Medicines Agency is also reviewing an application for licensure of V114 in adults.

October 20, 2020 - Merck announced Positive topline results from Two Additional Phase 3 Adult Studies Evaluating V114, Merck's Investigational 15-valent Pneumococcal Conjugate Vaccine. In the PNEU-PATH (V114-016) study, healthy adults 50 or older received V114 or PCV13, followed by PNEUMOVAX® 23 one year later. Following vaccination with PNEUMOVAX 23 (month 13), immune responses were comparable in vaccination groups for the 15 serotypes in V114. Results also showed that at 30 days post-vaccination with either V114 or PCV13 (day 30), immune responses were comparable for both groups across the 13 serotypes shared by the conjugate vaccines and higher in the V114 group for serotypes 22F and 33F, the two serotypes not included in PCV13.

January 30, 2019 - Merck announced that V114 received a Breakthrough Therapy Designation from the U.S. Food and Drug Administration (FDA) to prevent invasive IPD caused by the vaccine serotypes in pediatric patients six weeks to 18 years of age.

VAXNEUVANCE 15 Clinical Trials

Merck's V114 Pneumococcal Vaccine has undergone many clinical trials, and Merck continues to test the vaccine candidate under many scenarios. The registered 28 clinical trials can be accessed here.

VIMKUNYA® Chikungunya Vaccine Clinical Trials, Dosage, Efficacy, Indication, Side Effects 

Bavarian Nordic A/S VIMKUNYA® (Chikungunya Vaccine, Recombinant) CHIKV-VLP (PXVX0317) is a single-dose aluminum hydroxide-adjuvanted, non-live chikungunya virus-like particle vaccine (VLP) with a multi-protein structure that mimics the organization and conformation of naturally occurring viruses without the viral genome, promoting a more robust immune response and increased antibody production. Vimkunya vaccination triggers the production of neutralizing antibodies at 22 days and up to 183 days post-vaccination, which is expected to confer protection against chikungunya disease. Studies have shown that VLP vaccines are highly immunogenic, have a proven safety record, and typically elicit high-titer neutralizing antibodies, essential for protecting against the Chikungunya virus (CHIKV). The VLPs consist of CHIKV capsid protein (C) and envelope proteins E1 and E2 derived from the CHIKV Senegal strain 37997. VIMKUNYA™ is the first chikungunya vaccine to leverage VLP technology. It utilizes virus-like particles designed to mimic the chikungunya virus, but without the ability to infect cells, replicate, or cause disease. VIMKUNYA technology is licensed from the U.S. National Institute of Allergy and Infectious Diseases (NIAID) at the U.S. National Institutes of Health (NIH).

On February 14, 2025, the U.S. Food and Drug Administration (FDA) approved VIMKUNYA for injection, the first VLP chikungunya vaccine in the United States, for individuals 12 years of age and older. Concurrent with the approval, the FDA awarded Bavarian Nordic (BN) a Priority Review Voucher (PRV) under the Tropical Disease PRV program, which the Company intends to monetize when appropriate. On August 13, 2024, BN announced that the FDA had accepted and granted a Priority Review and Fast Track for the Biologics License Application for CHIKV VLP for individuals 12 and older. The FDA posted the Briefing Document on November 8, 2019. The FDA's approval of VIMKUNYA was based on data from two phase 3 studies that assessed the vaccine's effectiveness by measuring anti-chikungunya virus neutralizing antibody levels in over 3,500 healthy participants aged 12 years and older. On June 26, 2025, Dr. Lyle Petersen of the U.S. CDC presented this information during the ACIP vaccine meeting.

On March 7, 2025, BN announced that the UK Medicines and Healthcare products Regulatory Agency had validated the marketing authorization application and accepted it for review of VIMKUNYA. On February 28, 2025, BN announced that the European Commission had granted marketing authorization for VIMKUNYA in Europe for active immunization to prevent disease caused by the Chikungunya virus in individuals aged 12 years and older. Bavarian Nordic will launch VIMKUNYA in key European markets in the first half of 2025. The European Medicines Agency (EMA) granted PRIME designation in January 2020 (EMEA-002656-PIP01-19). Vimkunya was reviewed under the EMA's accelerated assessment program.

On May 12, 2025, a Journal Article concluded that CHIK-VLP provides approximately 95% overall short-term seroresponse rates in robust trials among potential travelers to CHIKV endemic areas, with an onset of seroprotection that may be as short as 8 days. On August 15, 2025, a study published in The Journal of Infectious Diseases provides the first in vivo evidence that CHIKV directly infects cartilage-producing chondrocytes, offering insights into the mechanisms of alphaviral arthritis.

Bavarian Nordic A/S is a fully integrated vaccine company headquartered in Denmark that develops, manufactures, and commercializes life-saving vaccines. Gaithersburg, Maryland-based Emergent BioSolutions sold this vaccine to Bavarian Nordic A/S on May 15, 2023. As of November 14, 2025, revenue for the first nine months of 2025 increased by 32% to DKK 4,793 million, reflecting a strong performance in both Travel Health and Public Preparedness. Travel Health revenue increased by 23% to DKK 2,327 million compared to the first nine months of 2024, primarily driven by increased demand for rabies and Tickborne encephalitis vaccines, and supported by the gradual launch of the chikungunya vaccine, Vimkunya®. Vimkunya's revenue was DKK 42 million in the first nine months of 2025.

VIMKUNYA Chikungunya Vaccine Availability 2025

As of 2025, VIMKUNYA is commercially available in various countries. VIMKUNYA is the first chikungunya vaccine approved in Europe, the UK, and the United States for individuals as young as 12 years old. As of November 2025, Vimkunya has also been launched in Sweden, Norway, Finland, Italy, and Spain in October.

On February 25, 2025, Bavarian Nordic announced a strategic partnership with Biological E. Limited to expand access to VIMKUNYA in low—and middle-income countries.

VIMKUNYA Efficacy

On April 19, 2025, The Lancet published results from a pivotal phase 3, randomized, double-blind, placebo-controlled, parallel-group trial, concluding that Vimkunya induces a rapid and robust immune response, supporting the potential for this vaccine to protect individuals aged 12–64 years from disease caused by the chikungunya virus.

U.S. CDC and VIMKUNYA

Bavarian Nordic announced on April 16, 2025, that the U.S. Centers for Disease Control and Prevention's (CDC) Advisory Committee on Immunization Practices (ACIP) voted to recommend VIMKUNYA for injection to prevent disease caused by the chikungunya virus. The ACIP recommends VIMKUNYA for individuals aged 12 and older traveling to a country or territory with a chikungunya outbreak. In addition, VIMKUNYA may be considered for persons traveling to or taking up residence in a country or territory without an outbreak but with an elevated risk for U.S. travelers, particularly if planning extended travel. The ACIP also recommends VIMKUNYA for laboratory workers with potential exposure to chikungunya. The HHS Secretary adopted these ACIP recommendations on May 13, 2025, and they are now official recommendations of the CDC.

VIMKUNYA Chikungunya Vaccine Indication

VIMKUNYA is indicated to prevent the Chikungunya virus, which is spread to people through infected mosquitoes. Symptoms lasting 3-4 weeks include high-grade fever, joint pain, headache, muscle pain, joint swelling, or rash. Chikungunya chronic arthralgia impacts a minority of patients but creates long-term health and work concerns. As of March 2025, Additional clinical studies are required to confirm the clinical profile of VIMKUNYA™, and confirmatory efficacy studies are also planned as part of the post-marketing commitments and requirements as agreed with the U.S. FDA.

VIMKUNYA Chikungunya Vaccine Dosage

VIMKUNYA is administered as a 40 µg dose by a muscular injection. VIMKUNYA is supplied as a single-dose, 1-mL glass prefilled syringe with a 0.8-mL dose volume. People with a lowered immune system, including people receiving medications that affect the immune system, may have a diminished response to VIMKUNYA™ vaccination.

VIMKUNYA Chikungunya Vaccine Side Effects

The most commonly reported adverse event in the clinical study was pain at the injection site, occurring in 12 (23%) of 53 participants who received the unadjuvanted vaccine (Group 1) and 111 (31%) of 356 who received the adjuvanted vaccine. No vaccine-related serious adverse events were reported. People should not receive VIMKUNYA if they are allergic to any of the vaccine ingredients or have had an allergic reaction following a previous dose of VIMKUNYA. 

VIMKUNYA Vaccination Recommendation

Chikungunya vaccination is recommended for adults traveling to a country or territory with a chikungunya outbreak. Since 2014, the U.S. CDC has reported Chikungunya virus disease cases among U.S. travelers returning from countries in the Americas where the virus is circulating. As of March 18, 2025, there have been Chikungunya outbreaks in numerous countries across Africa, the Americas, Asia, and Europe.

VIMKUNYA Revenues

Vimkunya's revenue from sales was DKK 5 million in the first quarter of 2025. The vaccine was launched in the U.S. in mid-March 2025, and the first European markets are expected to launch in the second quarter of 2025. On June 18, 2025, Bavarian Nordic announced that it had agreed to sell its Priority Review Voucher for a total cash consideration of $160 million, which will be recognized as other income.

VIMKUNYA Chikungunya Vaccine News

November 14, 2025 - Paul Chaplin, President & Chief Executive Officer of Bavarian Nordic, said: "Our travel health portfolio has shown continued strength, contributing to our best quarter for this business to date. 

July 31, 2025 - Bavarian Nordic A/S announced the completion of the sale of its Priority Review Voucher, for which the Company received a cash consideration of $160 million. 

July 22, 2025 - Paul Chaplin, President and CEO of Bavarian Nordic, said: "The regulatory submission and acceptance by Health Canada represent yet another highlight in our efforts to expand access to our chikungunya vaccine across the globe."

May 9, 2025 - Bavarian Nordic A/S announced its interim financial results and business progress for the first three months of 2025. Revenue for the first three months increased 62% to DKK 1,347 million, reflecting a strong performance in Travel Health and Public Preparedness.. Travel Health revenue increased by 52% to DKK 680 million.

April 16, 2025 - Paul Chaplin, President and CEO of Bavarian Nordic, stated: "The ACIP's recommendation of our chikungunya vaccine for Americans aged 12 and older represents a significant step forward in expanding access to this vaccine in the U.S."

March 27, 2025 - The Lancet published the results from a company-sponsored Phase 3 clinical study, which showed very positive outcomes.

March 18, 2025 - Lee Ann Kimak, Vice President of Commercial for North America at Bavarian Nordic, commented, "As the first virus-like particle single-dose, prefilled syringe chikungunya vaccine, VIMKUNYA™ provides a crucial new tool to help protect at-risk individuals traveling to regions where the virus is spreading."

March 7, 2025 - "Following the approvals of our Chikungunya vaccine in the US and EU last month, we are excited about the opportunity to expand its availability to European countries later this year," said Paul Chaplin, President and CEO of Bavarian Nordic.

March 5, 2025 - The Company stated: We have a leading commercialized portfolio of travel vaccines, and we continue to strengthen our position as a preferred supplier of mpox and smallpox vaccines to governments for public health preparedness.

February 28, 2025: Paul Chaplin, President and CEO of Bavarian Nordic, commented, "As we expand our presence across Europe, this vaccine will help further consolidate our leading position in travel vaccines. We look forward to making the vaccine available in key markets during the first half of 2025."

February 14, 2025 - Paul Chaplin, President and CEO of Bavarian Nordic, commented in a press release, "As climate change continues to expand the reach of mosquito-borne illnesses like chikungunya, this milestone underscores the importance of cutting-edge solutions to safeguard travelers and vulnerable populations."

January 31, 2025 - "The (EMA) recommendation of our chikungunya vaccine for approval in Europe marks a huge milestone in our efforts to deliver protection against this debilitating disease and, once approved, would represent a significant contribution to expanding the availability of vaccines to a broader population, including adolescents aged 12-17 years," said Paul Chaplin, President and CEO of Bavarian Nordic.

January 31, 2025 - Meeting highlights from the Committee for Medicinal Products for Human Use 27-30 January 2025.

August 13, 2024 - "The FDA review, along with the ongoing review of our CHIKV VLP vaccine by EMA, represents the first regulatory reviews of a chikungunya vaccine for adolescents, potentially providing a broader usage by populations at risk of this debilitating disease," commented Paul Chaplin, President and CEO of Bavarian Nordic.

July 18, 2024 - "The MAA submission and review marks a pivotal milestone for Bavarian Nordic in 2024, and we look forward to working closely with EMA throughout the evaluation process to make our chikungunya vaccine available to individuals 12 years of age and older at risk of chikungunya virus infection," said Paul Chaplin, President and CEO of Bavarian Nordic.

June 26, 2024 - "The MAA marks our second major submission in just a few weeks as part of our efforts to launch the Chikungunya vaccine next year in the U.S. and Europe," said Paul Chaplin, President and CEO of Bavarian Nordic, in a press release.

May 15, 2023: Bavarian Nordic acquired the rights to the development-stage Chikungunya vaccine candidate CHIKV VLP and manufacturing development facilities in Bern, Switzerland, and San Diego, California.

November 1, 2022 - Emergent BioSolutions Inc. announced results from a Phase 2 study evaluating the safety and immunogenicity of the CHIKV VLP vaccine candidate in prior recipients of other investigational alphavirus vaccines. The study demonstrated that the CHIKV VLP vaccine candidate was well-tolerated and immunogenic in alphavirus vaccine-naïve participants and participants previously vaccinated against the Venezuelan equine encephalitis virus. 

May 26, 2021 - Emergent BioSolutions Inc. announced two-year persistence data from its Phase 2 clinical study. Two years post-vaccination, SNA responses were 19 times higher than pre-vaccination titers following a single adjuvanted 40 µg dose of the CHIKV VLP vaccine, supporting the persistence of the immune response. All subjects in the single-dose regimen remained seropositive at their one-year and two-year visits. The vaccine candidate was well-tolerated, and no significant safety concerns related to the vaccine were identified.

January 13, 2020—Emergent BioSolutions Inc. announced that it had received an agreement from the European Medicines Agency to pursue its proposed development plan for its chikungunya virus-like particle (CHIKV VLP) vaccine candidate.

April 26, 2019 - Study published by PLOS: Vaccination with a chikungunya virus-like particle vaccine exacerbates disease in aged mice. Conclusions: Unadjuvanted CHIK VLP vaccination elicits immune responses that protect 100% of adult mice against CHIKV infection. However, an improved vaccine/adjuvant combination is still necessary to enhance the protective immunity against CHIKV in older people.

January 28, 2021 - A VLP vaccine for the epidemic Chikungunya virus protects non-human primates against infection.

CHIKV-VLP Clinical Trials

The CHIKV-VLP vaccine candidate is being investigated in various clinical trials in 2025. The approval of Vimkunya in 2025 was based on data from two phase 3 studies that assessed the vaccine's effectiveness by measuring anti-chikungunya virus-neutralizing antibody levels in over 3,500 healthy participants aged 12 years and older. Dr. Victoria Jenkins presented phase 3 clinical trial safety and efficacy data on CHIKV VLP at the Advisory Committee on Immunization Practices meeting on October 23, 2024.

On March 27, 2025, a company-sponsored Phase 3 study found that between May 12 and December 2, 2022, 413 participants were recruited and randomly assigned (1:1) to receive the Vimkunya vaccine (n = 206) or a placebo (n = 207). The coprimary endpoints of immunologic superiority were met, as measured by chikungunya virus SNA titers compared with placebo and the geometric mean titer at day 22. Vimkunya induced a protective seroresponse (SNA NT80≥100, considered the presumptive seroprotective antibody response) in 149 (82%) of 181 participants (95% CI 76·1–87·2) at day 15, in 165 (87%) of 189 participants (81·8–91·3) at day 22, and in 139 (76%) of 184 participants (68·9–81·2) at day 183. Although the early immune response was slightly higher in the 65–74 age group on day 15 than in the 75+ age group, the seroresponse rates on day 22 and day 183 were similar. There were no notable differences in adverse event rates between the groups; most adverse events were of grade 1 or 2 severity and had a short duration. No vaccine-related serious adverse events or deaths occurred.

The European Commission granted marketing authorization upon the recommendation of the Committee for Medicinal Products for Human Use of the European Medicines Agency in January 2025. It was based on results from two phase 3 clinical trials that enrolled more than 3,500 healthy individuals 12 years and older. The studies met their primary endpoints, with results showing that 21 days after vaccination, the vaccine-induced neutralizing antibodies were present in up to 97.8% of the vaccinated individuals, and a rapid immune response began to develop within one week.

ClinicalTrials.gov, NCT03992872 - Phase 2 Findings: Between November 20, 2019, and January 19, 2021, 60 participants (20 [33%] female and 40 [67%] male; 40 (67%) White; median age 47·0 years [IQR 13·5]), 30 previous alphavirus vaccine recipients and 30 alphavirus vaccine-naïve controls, were enrolled, vaccinated with CHIKV VLP, and completed the trial. The anti-CHIKV neutralizing antibody seroconversion rate at day 22 was 100% (95% CI 88·6-100) in both groups. GMTs peaked in previous alphavirus vaccine recipients and alphavirus vaccine-naïve controls at day 22 (2032·5 [95% CI 1413·0-2923·6] and 2299·2 [1598·1-3307·8], respectively) and were similar between the groups on day 22 and all subsequent visits. A higher proportion of previous alphavirus vaccine recipients (93·3% [95% CI 78·7-98·2]) had a four-fold neutralizing antibody increase at day 8 than did alphavirus vaccine-naïve controls (66·7% [48·8-80·8]; p=0·021). There was no statistically significant difference in the incidence of solicited adverse events between the previous alphavirus vaccine recipients and the alphavirus vaccine-naïve controls (53.3% vs. 40.0%, respectively). However, the relatively small sample size of the trial limited the power to detect a significant difference. No serious adverse events were reported with the vaccine. Interpretation: The CHIKV VLP vaccine was well tolerated and demonstrated similar immunogenicity in alphavirus-naïve participants and those who had previously received a heterologous alphavirus vaccine. There were no significant differences in adverse events between the groups. The results of this study support the use of the CHIKV VLP vaccine in individuals with prior exposure to alphavirus vaccines.

According to a study presented in October 2023, the researchers assessed anti-CHIKV serum-neutralizing antibody titers at designated time points throughout the study. They determined the seroresponse rate (SRR) in the two cohorts. In total, 3,254 participants were enrolled in the adult and adolescent trial, of whom 2,790 received a CHIKV VLP dose and 464 received a placebo. The data showed an SRR of 98% on day 22 for the vaccine and 1% for the placebo. A rapid antibody response was also observed in the vaccine group, with an SRR of 47% on day 8 and 97% on day 15. These responses remained durable through day 183, when the SRR reached 86%. For the older adult trial, 413 participants were enrolled — 206 received CHIKV VLP, and 207 received a placebo. On day 22, the SRR was 87% for vaccine recipients and 1% for placebo recipients. By day 15, a rapid antibody response was also observed in the CHIKV VLP group, with a seroprotection rate (SRR) of 82%. Additional data from the study revealed a favorable safety profile for the vaccine, with most adverse events being mild to moderate in severity. The most common adverse events were myalgia, fatigue, and headache.

On June 20, 2023, the Company announced the phase 3 study results, which included 413 participants enrolled and randomized 1:1 to receive either a single intramuscular injection of CHIKV VLP or a placebo. The initial results up to Day 22 post-vaccination showed that CHIKV VLP was immunogenic in healthy adults ≥65 years of age, as demonstrated by a strong induction of CHIKV neutralizing antibodies in 87% of vaccinees with neutralizing antibody titers exceeding the threshold agreed with authorities as a marker of seroprotection, thus meeting the primary endpoints of the study. Notably, most subjects (82%) also had seroprotective neutralizing antibodies on Day 15 post-vaccination, demonstrating a rapid onset of protection for the VLP-based CHIKV vaccine candidate.

On August 6, 2023, Bavarian Nordic (BN) announced positive topline results from a Phase 3 clinical trial (NCT05072080). PXVX0317 met all the coprimary endpoints and was highly immunogenic in the majority of subjects 22 days after a single vaccination. A rapid and durable response was confirmed, with high immunity levels at 2 weeks and 6 months post-immunization.

On November 14, 2022, the Company announced that a planned post-approval multicenter Phase 3b clinical study will evaluate the vaccine candidate's efficacy in preventing CHIKV disease and assess the utility of a model-guided disease surveillance framework to optimize the execution of a field efficacy trial using CHIKV as a model emerging pathogen.

On November 1, 2022, the Company reported a Phase 2 parallel-group study—a gender-matched, open-label study evaluating the safety and immunogenicity of an adjuvanted CHIKV VLP vaccine candidate in individuals who had previously received experimental alphavirus vaccines, compared with a cohort of individuals naïve to alphavirus vaccines. The study enrolled 60 healthy adults at two U.S. sites. The vaccine candidate was well-tolerated, with no notable difference in the incidence of adverse events between the groups. The majority of solicited adverse events were mild or moderate. The most common adverse event was local injection site pain. The seroconversion rate 21 days post-vaccination was 100% in both groups. A higher percentage of prior alphavirus vaccine candidates showed a fourfold or greater increase on study day eight, narrowing the difference between the alphavirus vaccine-naïve group.

A randomized, double-masked, parallel-group, Phase 2 study was conducted at three U.S. sites involving 445 participants. Eligible participants were healthy CHIKV-naïve adults aged 18–45 years. The primary endpoint was the geometric mean titer of the anti-CHIKV neutralizing antibody on day 57 (28 days after the last vaccination). Safety was also assessed.