IXCHIQ® Chikungunya Vaccine (VLA1553) Clinical Trials, Dosage, Efficacy, Indication, Side Effects

Valneva SE's IXCHIQ® Chikungunya Vaccine, Live (VLA1553) is the first approved monovalent, single-dose, live-attenuated vaccine. As of 2023, IXCHIQ® was the first vaccine approved to address chikungunya virus (CHIKV) infections in adults at increased risk of exposure to the mosquito-transmitted disease. IXCHIQ is based on an infectious clone (CHIKV LR2006-OPY1) attenuated by deleting a significant gene encoding the non-structural replicase complex protein nsP3 protection against various Chikungunya virus (CHIKV) phylogroups and strains. IXCHIQ is designed for prophylactic, active immunization against CHIKV infections in humans over 1-year-old. Recombumin®, a chemically defined, human and animal origin-free recombinant human albumin, is an enabler for the manufacture and formulation of IXCHIQ. 

IXCHIQ was approved by the U.S. Food and Drug Administration (FDA, STN: 125777) on November 9, 2023. The FDA's Summary Basis for Regulatory Action was posted on December 8, 2023. This indication was approved under FDA-accelerated approval based on anti-CHIKV neutralizing antibody titers. IXCHIQ achieves target immunogenicity with a single dose. Valneva announced on December 3, 2024, that among the 278 healthy adults still enrolled in a clinical trial, 96% maintained neutralizing antibody titers well above the seroresponse threshold three years after the single-dose vaccination. The FDA awarded Valneva a tropical disease priority review voucher under a 2007 provision in the FDA Amendments Act. In 2021, the IXCHIQ vaccine program received FDA Fast Track (2018) and Breakthrough Therapy designations. The FDA published complete prescribing information at this link. The U.S. Defense Health Agency – Immunization Healthcare Division published guidance authorizing IXCHIQ® as a U.S. Department of Defense CHIKV countermeasure.

The U.S. Centers for Disease Control and Prevention (CDC) Advisory Committee on Immunization Practices (ACIP) approved recommendations for using IXCHIQ in travelers and laboratory workers in February 2024. On October 23, 2024, the ACIP reviewed an IXCHIQ update - Long-term persistence clinical trial is ongoing; High seroresponse rate (97%) at 2 years; Monitoring continuing through 10 years to determine if booster dose needed in future. The CDC issued an updated Level 2 Travel Health Advisory confirming that chikungunya vaccination is recommended for adults traveling to a destination with a current chikungunya outbreak.

On February 28, 2025, Valneva SE announced that the Committee for Medicinal Products for Human Use (CHMP) of the European Medicines Agency (EMA) adopted a positive opinion recommending authorization of a label extension for IXCHIQ® to individuals 12 years of age and older. IXCHIQ® received European marketing authorization for individuals 18 and older in July 2024.

Saint-Herblain, France-based Valneva SE (Nasdaq: VALN; Euronext Paris: VLA) is a specialty vaccine company that provides prevention against diseases with significant unmet medical needs. Valneva's commercial portfolio is composed of three travel vaccines: IXIARO®/JESPECT®, DUKORAL®, and IXCHIQ®. The Company's 2023 Sustainability Report includes activities during 2023 and prospective priorities and is by French Decree No. 2017-1265 of August 9, 2017. On April 3, 2024, Valneva announced it won the Best Prophylactic Vaccine at the Vaccine Industry Excellence Awards 2024. Valneva won the Breakthrough of the Year on June 14, 2024, for its Chikungunya vaccine at the 2024 European Mediscience Awards.

IXCHIQ Vaccine Efficacy

On January 20, 2025, Valneva SE reported IXCHIQ® showed a sustained 98.3% sero-response rate one year after a single vaccination. The Lancet Infectious Disease published results from a phase 3b study that concluded that after a single VLA1553 vaccination, chikungunya virus-neutralizing antibodies were above the threshold considered to be protective and persisted for up to two years. There were no long-term serious adverse events related to vaccination.

IXCHIQ Vaccine Availability

As of March 11, 2025, IXCHIQ was available for adults in the U.S., Asia, Canada, Europe, and the Virgin Islands. On May 31, 2024, the European Commission (EMA/271910/2024) recommended the vaccine. On February 4, 2025, the UK's Medicines and Healthcare Products Regulatory Agency approved IXCHIQ to protect adults against chikungunya disease. On December 19, 2024, Valneva SE and Serum Institute of India (SII) announced an exclusive license agreement to supply IXCHIQ in Asia. As of 2025, the Brazilian Health Regulatory Agency (Anvisa) is reviewing IXCHIQ's marketing application. To make the vaccine more accessible to Low- and Middle-Income Countries, Valneva and Instituto Butantan in Brazil signed an agreement in January 2021 to develop, manufacture, and market VLA1553.

IXCHIQ Vaccine CHIKV Cross-Neutralization

A Research Article published on March 10, 2025, analyzed plaque reduction neutralization of three CHIKV lineages, namely the East Central South African, the West African, and the Asian lineage, which were inhibited by CHIKV-specific neutralizing antibodies present in the sera from vaccinated humans. This effect was independent of the time elapsed since vaccination. Moreover, the magnitude of the immune response was similar to the antibody levels detected in sera from convalescent chikungunya patients.

IXCHIQ Vaccine U.S. CDC Reviews

The U.S. CDC website stated that, in February 2025, the agency is currently investigating hospitalizations for cardiac or neurologic events following vaccination with IXCHIQ among people 65 years of age and older. On June 26, 2024, the U.S. CDC Advisory Committee on Immunization Practices (ACIP) reviewed the following IXCHIQ and Chikungunya virus presentations. On February 28, 2024, the ACIP reviewed Key points from FDA licensure and package insert, a review of proposed policy options for chikungunya vaccine use among U.S. adults traveling abroad, a review of proposed policy options for chikungunya vaccine use among laboratory workers, and vaccine use among pregnant and breastfeeding women. On February 29, 2024, Valneva SE announced that the ACIP voted to recommend the use of IXCHIQ® for the prevention of diseases caused by CHIKV.

Dr. Beth Bell presented proposed policy options for chikungunya vaccine use among U.S. adults traveling abroad at the ACIP meeting on October 26, 2023. On June 22, 2023, the ACIP reviewed the following presentations: ACIP Work Group timeline (tentative); Value of a vaccine to prevent travel-related Chikungunya for U.S. persons. On February 23, 2023, ACIP presentations included: Introduction by Dr. Beth Bell; Global Epidemiology of Chikungunya; Dr. Susan Hills; Chikungunya in U.S. travelers, Ms. Nicole Lindsey; Persistent arthralgia following Chikungunya, Ms. Nicole Lindsey; Workgroup considerations, Ms. Nicole Lindsey. During the ACIP meeting on October 19, 2022, Katrin Dubischar, VP and Program Director of Chikungunya Vaccine, delivered the VLA1553 Chikungunya Vaccine Candidate Introduction, Evidence Supporting the Serological Endpoint, and Clinical Study Overview. VLA1553 is an efficient and safe intervention that offers high seroprotection against chikungunya virus infection, a virus likely to spread globally with an urgent demand for long-lasting prophylaxis.

The U.S. CDC published recommendations for using the Chikungunya vaccine among adult travelers: ACIP recommends the Chikungunya vaccine for persons aged ≥18 years traveling to a country or territory with a Chikungunya outbreak. In addition, the Chikungunya vaccine may be considered for those traveling to a country or territory without an outbreak but with evidence of Chikungunya virus transmission among humans within the last five years. Persons aged >65 years, particularly those with underlying medical conditions, are likely to have at least moderate exposure* to mosquitoes or Persons staying for a cumulative period of 6 months or more. Moderate exposure could include travelers with at least two weeks (cumulative) of exposure to mosquitoes in indoor or outdoor settings.

IXCHIQ Vaccine Pediatric

On January 22, 2025, Valneva announced that VLA1553-221 met its primary endpoint, demonstrating that the vaccine was well tolerated by children aged one to eleven years regardless of the dose (half dose or full dose) or previous CHIKV infection and, to a similar extent, to an active control MenACYW vaccine. Overall, the safety profile was consistent with the profile observed in Valneva's pivotal Phase 3 trials in adults and adolescents. An independent Data Safety Monitoring Board confirmed the absence of any safety concerns. Valneva's vaccine was highly immunogenic in both dose groups. A full dose of the vaccine exhibited a more robust immune response than a half dose by providing protective antibody titers already at Day 15 and Day 29 post-vaccination, confirming the excellent Immunogenicity previously observed in adults and adolescents.

On January 10, 2024, Valneva announced that the first participant had been vaccinated in a Phase 2 clinical trial evaluating the safety and Immunogenicity in children of two different doses of Valneva's single-shot chikungunya vaccine. On December 4, 2023, Valneva reported a 97% seroresponse rate 24 months after a single vaccination with IXCHIQ and no safety concerns. On November 13, 2023, Valneva reported positive pivotal Phase 3 immunogenicity data in adolescents. VLA1553, administered as a single dose, was generally well tolerated in adolescents aged 12 to <18 years, irrespective of previous CHIKV infection, and showed a similar safety profile as reported in adults. These results complement the initial Phase 3 safety data the Company reported for the trial in August 2023.

IXCHIQ Vaccine Indication

The U.S. CDC says vaccination is recommended for adults aged 18 years and older traveling to a country with a chikungunya outbreak. Over 50 million North Americans, including approximately 7 million Canadians, travel to countries where Chikungunya is endemic. Chikungunya outbreaks continue to occur with changing epidemiology. Awareness about Chikungunya among at-risk travelers and healthcare professionals can result in underdiagnosis and underreporting. While mortality due to CHIKV infection is low, the morbidity and overall burden of the disease are high. After the acute disease phase, chronic sequelae, including persistent arthralgia, are common, with around 40% of people infected with CHIKV developing chronic post-CHIK arthritis, which may last for months or years. A study reported in December 2024 that Chikungunya chronic arthralgia impacts long-term health and work.

XCHIQ targets long-term protection against the Chikungunya virus in adults following vaccination. However, vaccination with IXCHIQ may not protect all individuals. 

IXCHIQ Vaccine Dosage

VLA1553 is administered intramuscularly with a single dose. At clinical trial centers in Illinois and Alabama, U.S., healthy volunteers aged 18–45 years were randomly assigned (1:1:2) to one of three escalating groups (low dose 3·2 × 10^3 per 0·1 mL; medium dose 3·2 × 10^4 per 1 mL; or high dose 3·2 × 10^5 50% tissue culture infection dose per 1 mL) and received a single-shot immunization on day 0. Individuals in all groups were revaccinated with the highest dose on either month 6 or 12 and followed for 28 days after revaccination.

IXCHIQ Vaccine Contraindications

IXCHIQ® should not be given to individuals who have a weakened immune system due to medications used for hematologic and solid tumors, are on chemotherapy, have a history of congenital immunodeficiency, are under long-term immunosuppressive therapy, or have an HIV infection and are severely immunocompromised—individuals with a history of a severe allergic reaction to any vaccine component.

IXCHIQ Vaccine Warnings

On October 14, 2024, a study concluded, 'A single dose of VLA1553 presented with an excellent local tolerability profile and overall safety in line with that expected for a live-attenuated vaccine.' Common adverse reactions following vaccination that occurred in >10% of vaccinated persons in clinical trials included tenderness, headache, fatigue, myalgia, arthralgia, fever, and nausea. IXCHIQ also caused severe or prolonged chikungunya-like adverse reactions in some persons. Appropriate medical treatment to manage immediate allergic reactions for acute anaphylactic reactions following the administration of IXCHIQ® or any vaccine must be available, says the FDA. Vaccination with IXCHIQ® may cause severe or prolonged chikungunya-like adverse reactions. Severe chikungunya-like adverse reactions that prevented daily activity and/or required medical intervention occurred in 1.6% of 3,082 IXCHIQ® recipients and no placebo recipients. Fourteen IXCHIQ® recipients had prolonged (duration at least 30 days) chikungunya-like adverse reactions. The most common injection site reaction (>10%) was tenderness (11%), and the most common systemic adverse reactions (>10%) were headache (31%), fatigue (29%), myalgia (24%), arthralgia (17%), fever (13%) and nausea (11%)

IXCHIQ Vaccine Pregnancy And Lactation 

There are no adequate and well-controlled studies of IXCHIQ® in pregnant individuals, and human data available from clinical trials with IXCHIQ® are insufficient to establish the presence or absence of vaccine-associated risk during pregnancy. In general, vaccination should be deferred until after delivery. However, if pregnant women choose to be vaccinated, out of caution, vaccination should generally be avoided during the 1st trimester (until 14 weeks gestation) and after the 36th week of gestation. A developmental study was conducted in female rats. IXCHIQ® should be administered during pregnancy only after an individual risk-benefit assessment, considering the maternal risk of chikungunya infection and gestational age. Vertical transmission of wild-type CHIKV to neonates from pregnant women with viremia at delivery is standard and can cause severe, potentially fatal CHIKV disease in neonates. Human data are not available to assess the impact of IXCHIQ on milk production, its presence in breast milk, or its effects on the breastfed child.

IXCHIQ Immunocompromised Individuals

Due to disease or medical therapy, IXCHIQ should not be administered to immunodeficient or immunosuppressed individuals.

IXCHIQ Vaccine Efficacy Against Alphaviruses

Alphaviruses are vector-borne, medically relevant, positive-stranded RNA viruses that cause human disease worldwide. A study published on August 7, 2024, characterized nAbs against CHIKV strains. IXCHIQ elicited 100% seroconversion to each virus, except for RRV at 83.3% seroconversion of vaccinees, and cross-neutralizing antibody potency decreased with increasing genetic distance from CHIKV. These data suggest that IXCHIQ efficiently and potently elicits cross-nAb breadth that extends to related alphaviruses similar to natural CHIKV infection. The journal Science Translational Medicine published a Research Article, Vol 15, Issue 696, on May 17, 2023, which found that MAbs with the most significant passive protective efficacy in a mouse model of CHIKV also protected against related arthritogenic alphaviruses.

IXCHIQ Vaccine Coadministration

The Company has not disclosed coadministration information.

IXCHIQ Vaccination for Laboratory Staff

According to the CDC, chikungunya vaccination is recommended for laboratory workers who may be exposed to the virus. Transmission through the aerosol and percutaneous routes of the virus has been documented in the laboratory setting, and accidental mucosal exposure is possible. Laboratory work with the Chikungunya virus is restricted to biosafety level-3 (BSL-3) facilities and practices.

Chikungunya Outbreaks

Countries in Asia, Europe, and the Americas confirmed Chikungunya virus outbreaks in 2025, 2024, and 2023.

Valneva SE Agreements with CEPI

The Coalition for Epidemic Preparedness Innovations (CEPI) and Valneva SE announced on July 22, 2024, that they have expanded their partnership to support broader access to IXCHIQ® in Low—and Middle-Income countries (LMICs), as well as post-marketing trials and potential label extensions in children, adolescents, and pregnant women. CEPI will provide Valneva up to U.S. $41.3 million of additional funding over the next five years, with support from the European Union's (EU) Horizon Europe program. An earlier CEPI agreement awarded Valneva U.S. $24.6 million in CEPI-EU funding to develop, manufacture, and market its single-shot vaccine in certain LMICs affected by Chikungunya.

Valneva SE Financial News

On March 3, 2025, Valneva SE announced that its senior management will participate at the TD Cowen 45th Annual Health Care Conference, taking place March 3 – 5, 2025, in Boston, MA, and the Van Lanschot Kempen Life Sciences Conference, held April 2 – 3, 2025, in Amsterdam, The Netherlands.

Valneva announced on February 18, 2025, that it met its 2024 growth targets for sales revenue (+13% compared to 2023) and total revenues (+10% compared to 2023), maintaining a strong year-end cash position of €168.3 million.

On November 7, 2024, Valneva announced total revenues of €116.6 million, including product sales of €112.5 million and IXCHIQ initial sales of €1.8 million in the first nine months of 2024. The operating profit was €34.2 million compared to an operating loss of €57.2 million in the first nine months of 2023.

Valneva and the Butantan Institute in Brazil signed a term sheet in May 2020 to develop, manufacture, and market VLA1553. The collaboration is part of the $23.4 million funding framework that Valneva received from the CEPI in July 2019 to make VLA1553 accessible to Low —and Middle-Income Countries. As of July 22, 2024, Valneva will receive up to $41.3 million from CEPI and the European Union. On February 5, 2025, CEPI reaffirmed its work, focusing on expanding access to vaccine doses at an affordable price in those endemic regions.

IXCHIQ Vaccine News

February 28, 2025 - Juan Carlos Jaramillo, M.D., Chief Medical Officer of Valneva, said, “Broader accessibility will help provide protection and mitigate the burden of this debilitating illness, which is continuing to spread in previously unaffected areas.”

February 25, 2025 - The CDC investigates hospitalizations for cardiac or neurologic events following vaccination with IXCHIQ.

February 18, 2025: Peter BühlValneva'sva's Chief Financial Officer commented, "Once again, we successfully delivered double-digit sales growth... We made significant clinical and regulatory progress last year, setting the stage for several important catalysts to drive value in 2"25."

February 4, 2025: Julian Beach, MHRA Interim Executive Director of Healthcare Quality and Access, said in a press release, "Patient safety is our top priority, which is why I am pleased to confirm the approval of the first vaccine in the UK to protect adults 18 years and older against Chikungunya."

January 22, 2025 - Juan Carlos Jaramillo, M.D., Chief Medical Officer of Valneva, said, "These first data in children are aligned with the robust antibody response and good safety profile we reported in both adolescents and adults after a single vaccination ."

December 3, 2024—Juan Carlos Jaramillo, M.D., Chief Medical Officer of Valneva, said in a press release, "We are extremely pleased about these three-year data, which further highliIXCHIQ®'sQ®'s differentiated product profile and ability to induce a robust, long-lasting antibody response in both younger and older adults with a single vaccination. 

September 4, 2024: The Lancet published a Comment stating that an effective chikungunya vaccine would reduce the burden of acute infections and mitigate the substantial loss of economic productivity in working-age adults.

July 22, 2024—Thomas Lingelbach, Chief Executive Officer of Valneva, said, "We are extremely pleased to strengthen our partnership with CEPI." Valneva will receive up to $41.3 million from CEPI and the European Union to expand access to the chikungunya vaccine, IXCHIQ®.

July 1, 2024: Dr. Richard Hatchett, CEO of the Coalition for Epidemic Preparedness Innovations, comments, "Supported by CEPI and EU funding, IXCHIQ is the world's first vaccine offering protection against the debilitating CHIKV." 

May 21, 2024 – Valneva SE announced the appointment of Dr. Hanneke Schuitemaker, Ph.D., as Chief Scientific Officer and Executive Committee member, effective June 3, 2024.

January 10, 2024 - Juan Carlos Jaramillo, M.D., Chief Medical Officer of Valneva, said, "This pediatric clinical trial is significant. Given the significant threat that ChikChikungunyaes poses to individuals living in or traveling to endemic areas, it is crucial to make the vaccine accessible to all age groups."

October 19, 2022 - The U.S. CDC vaccine committee reviews various presentations, such as OVERVIEW OF CHIKUNGUNYA AND CHIKUNGUNYA VACCINES by Susan Hills, MBBS, MTH CDC Lead, Chikungunya Vaccines Work Group.

July 7, 2021 - Valneva SE announced that the U.S. FDA had awarded Breakthrough Therapy Designation for VLA1553.

January 25, 2021: Valneva SE and Instituto Butantan signed definitive agreements to develop, manufacture, and market Valneva's single-shot chikungunya vaccine, VLA1553, in Low —and Middle-Income Countries.

October 16, 2020 - Valneva SE announced that the European Medicines Agency had granted PRIority MEdicines designation for VLA1553.

December 21, 2018 - The U.S. Food and Drug Administration granted VLA1553 Fast Track designation. 

VLA-1553 Clinical Trials

Valneva continues to test the VLA1553 Chikungunya Vaccine in various clinical triaIXCHIQ®'sQ®'s final pivotal Phase 3 data were published in The Lancet in June 2023.

A clinical study in adolescents, VLA1553-321, is ongoing. Additionally, the Company initiated a Phase 2 pediatric trial, VLA1553-221, in children aged 1 to 11 in January 2024. This is designed to support a Phase 3 pivotal pediatric study and potentially extend the label to this age group following initial regulatory approvals in adults and possibly adolescents.

Phase 2 Trial VLA1553-221 is a multicenter, randomized, observer-blinded, dose-response Phase 2 clinical trial in approximately 300 healthy children aged one to eleven. It will be performed at three sites in the Dominican Republic and potentially Honduras. The primary and secondary objectives of the trial are to evaluate the safety and Immunogenicity of two different dose levels of Valneva's single-shot chikungunya vaccine. Additional information, including a detailed description of the trial design, eligibility criteria, and investigator sites, is available at ClinicalTrials.gov (Identifier: NCT06106581).

The VLA1553-321 study in Brazil, posted on August 28, 2023, is a prospective, double-blinded, multicenter, randomized, placebo-controlled, pivotal Phase 3 trial conducted in 754 adolescents aged 12 to 17 years old in Brazil. The VLA1553-321 clinical trial was initiated in January 2022, and Valneva reported enrollment and vaccination completion in February 2023. VLA1553 or placebo was administered as a single intramuscular immunization to randomized participants in two study groups at a 2:1 ratio. The primary objective is to evaluate the Immunogenicity and safety of the adult dose of VLA1553 28 days following a single vaccination. Secondary objectives of the trial include assessment of safety and Immunogenicity up to twelve months following a single immunization with VLA1553. The study will also provide safety and immunogenicity data in participants previously exposed to ChikChikungunya. On June 13, 2023, the phase 3 study results were published: Between September 17, 2020, and April 10, 2021, 6,100 people were screened for eligibility. One thousand nine hundred seventy-two people were excluded, and 4128 participants were enrolled and randomized (3093 to VLA1553 and 1035 to placebo). 358 participants in the VLA1553 group and 133 in the placebo group discontinued before the trial ended. The per-protocol population for immunogenicity analysis comprised 362 participants (266 in the VLA1553 group and 96 in the placebo group). After a single vaccination, VLA1553 induced seroprotective chikungunya virus neutralizing antibody levels in 263 (98·9%) of 266 participants in the VLA1553 group (95% CI 96·7–99·8; p<0·0001) 28 days post-vaccination, independent of age. VLA1553 was generally safe, with an adverse event profile similar to other licensed vaccines, and was equally well tolerated in younger and older adults. Serious adverse events were reported in 46 (1·5%) of 3082 participants exposed to VLA1553 and eight (0·8%) of 1033 participants in the placebo arm. Only two serious adverse events related to VLA1553 treatment (one mild myalgia and one syndrome of inappropriate antidiuretic hormone secretion) were considered. Both participants recovered fully.

On December 5, 2022, the Company announced that the antibody persistence trial enrolled 363 healthy adult participants, following them from month six after vaccination to month twelve. 99% of participants retained neutralizing antibody titers above the seroresponse threshold of 150 12 months after the single-dose vaccination. These antibody levels confirm the antibody persistence profile observed in an earlier study. In addition, the antibody persistence was similar in older adults aged ≥65 years, who retained neutralizing antibody titers comparable to younger adults throughout the follow-up. These results follow the completion of the pivotal study VLA1553-301, for which a seroresponse rate of 96% was reported six months after vaccination.

VLA1553-301 Phase 3 trial was initiated in September 2020. It is a prospective, double-blinded, multicenter, randomized, pivotal Phase 3 trial evaluating 4,115 participants aged 18 years or above. Lyophilized VLA1553 or placebo was administered as a single intramuscular immunization. The trial's primary objective was to assess the Immunogenicity and safety of VLA1553 in one month following a single vaccination. 

Conducted in Brazil by Instituto Butantan, VLA1553-321 is a double-blinded, multicenter, randomized, and placebo-controlled Phase 3 trial. Seven hundred fifty adolescents aged 12 to 1s will be randomized at a 2:1 ratio to receive either VLA1553 or a placebo. The trial's primary objective is to evaluate safety and Immunogenicity following a vaccination with VLA1553. Participants will be assessed after 28 days and followed up to twelve months. The study will also provide safety and immunogenicity data in participants previously exposed to Chikungunya.

In 20VLA1553's53's complete Phase 1 clinical trial data were published in the peer-reviewed medical journal The Lancet Infectious Diseases. On May 5, 2022, Valneva confirmed that the Coalition for Epidemic Preparedness Innovations (CEPI) funded a phase 3 clinical study and reported positive topline lot-to-lot manufacturing consistency trial results for VLA1553. An analysis announced on March 8, 2022, confirmed the very high level of seroprotection, with 98.9% of participants achieving protective levels of CHIKV-neutralizing antibodies one month after receiving a single vaccination. In addition, the immunogenicity profile was maintained over time, with 96.3% of participants showing protective CHIKV-neutralizing antibody titers six months after receiving a single immunization. 

On May 13, 2024, an analysis of study VLA1553-321 Day 180 results confirmed the initial positive Immunogenicity and safety data Valneva reported previously and are intended to support filing for potential label extension for use in adolescents aged 12 to 17 years. On September 4, 2024, The Lancet published results from a CEPI and EU Horizon 2020-funded phase 3 study conducted in Brazil. The study concluded that VLA1553 was generally safe and induced seroprotective titers in almost all vaccinated adolescents, with favorable safety data in seropositive adolescents at baseline. The data support using VLA1553 to prevent diseases caused by the Chikungunya virus among adolescents and in endemic areas.