FDA Suspends Chikungunya Vaccine Over Safety Concerns

The U.S. Food and Drug Administration (FDA) announced on Aug. 22, 2025 that it has suspended the license for French drugmaker Valneva’s chikungunya vaccine, warning that its continued use “poses a danger to public health” following a risk–benefit analysis conducted by the agency’s Center for Biologics Evaluation and Research (CBER). The decision came after reports of serious adverse events—including two deaths—among adults 60 and older, which led the FDA and the U.S. Centers for Disease Control and Prevention (CDC) to pause administration of the vaccine in May 2025 while investigating.^{1 2}

The vaccine, Ixchiq, is a live attenuated virus vaccine that first received FDA licensure under an accelerate approval pathway in November 2023 to prevent chikungunya, a mosquito-borne illness marked by fever, severe joint pain, and in rare cases, long-lasting disability. Although the FDA lifted the pause on Aug. 6, it restricted the vaccine’s use to people considered at high risk of exposure to the virus. According to the CDC, those at greatest risk of severe disease include older adults, newborns infected around the time of birth, pregnant women, and individuals with underlying conditions such as diabetes, heart disease, or high blood pressure.³

FDA: At Least One Death Linked to Vaccine-Induced Encephalitis

In a news release, the FDA reported one death from encephalitis (inflammation of the brain) directly linked to the vaccine, along with more than 20 serious adverse events described as “chikungunya-like illness,” including 21 hospitalizations and three deaths.¹

Like other live attenuated vaccines, Ixchiq contains a weakened form of the chikungunya virus intended to stimulate the immune system without causing full-blown disease. Because live attenuated vaccines can cause side effects that resemble the illness itself, some of the reported cases of “chikungunya-like illness” following Ixchiq vaccination may reflect immune responses to the vaccine rather than naturally acquired infections.⁴

Benefits of Ixchiq Vaccination No Longer Outweigh the Risks

The FDA noted that symptoms such as fever, headache, muscle or joint pain, and fatigue are consistent both with chikungunya disease and with known reactions to live attenuated vaccines, making them difficult to distinguish in practice. In its May 9, 2025 safety communication announcing a pause in vaccination for older adults, the agency stated, “Ixchiq contains a live, weakened version of the chikungunya virus and may cause symptoms similar to those of chikungunya disease.”²

In an Aug. 22 update, the FDA concluded that the benefits of Ixchiq no longer outweigh the risks. The agency emphasized that the vaccine’s clinical benefit has not been verified in studies and that its benefit–risk analysis “broadly shows the vaccine does not have benefits outweighing risks, under most plausible scenarios.”⁵

Chikungunya Virus Rarely Causes Serious Problems or Death: Mayo Clinic

According to the CDC, chikungunya is spread by Aedes mosquitoes, the same species responsible for transmitting Zika, dengue, and yellow fever. These mosquitoes thrive in warm, humid environments commonly found in southern states, particularly along the Gulf Coast, making travelers, outdoor workers, and residents in these regions more susceptible. Before the suspension of the license, it was recommended that Americans traveling to areas where chikungunya outbreaks were occurring to get the vaccine.⁶

The Mayo Clinic recognizes that the virus rarely causes serious problems or death, and most people who contract the virus recover within a week, although the joint pain can persist for months or years. To manage any lingering joint pain, patients are often prescribed arthritis medications, which carry risks separate from the live vaccine, such as gastrointestinal bleeding, liver damage, or increased cardiovascular risk.⁷

Valneva Downplays Reports of Serious Adverse Events

Valneva responded to the FDA’s suspension by noting that the decision came shortly after the agency had lifted its earlier pause on Aug. 6. The drugmaker said that the FDA based its updated action on new data from the Vaccine Adverse Event Reporting System (VAERS), which included four additional serious adverse events reported outside the United States. Valneva said the cases—three in patients aged 70 to 82 and one in a 55-year-old—were “consistent with those previously reported during clinical trials and post-marketing experience.” The European Medicines Agency (EMA) had taken a similar step in May, temporarily restricting use of Ixchiq in adults 65 and older, though the EMA lifted that pause on July 25.^{1 8}

Valneva’s messaging shifted between the two regulatory actions: when the FDA first paused the vaccine for older Americans in May 2025, the company suggested the reactions could be tied to recipients’ underlying health conditions or interactions with other medications. In August, however, Valneva acknowledged the new reports of serious side effects and deaths—still in this same age group—but framed them as “expected” within the context of clinical trial and post-marketing data.^{7 8}

In its statement, Valneva emphasized its intent to continue advancing Ixchiq despite the licensure setback, citing that the chikungunya virus—which the Mayo Clinic acknowledges rarely causes serious injury or death—is a “clear threat.” Valneva CEO Thomas Lingelbach said, “As we determine potential next steps, and as the clear threat of chikungunya continues to escalate globally, Valneva remains fully committed to maintaining access to our vaccine as a global health tool for addressing and preventing outbreaks of this devastating illness.”⁸

The company’s press release concluded not with a focus on patient safety but with financial updates to shareholders, noting that Valneva is “evaluating the potential financial impact of a permanent withdrawal of the IXCHIQ® license in the United States, but is not modifying its revenue guidance at this time.” In closing, the statement highlighted that Ixchiq generated €7.5 million of the company’s €91 million in total product sales in the first half of 2025, much of it tied to a one-time vaccine delivery for the African outbreak.⁸

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