FDA Suspends Biologics License for Chikungunya Virus Vaccine Following Reports of Encephalitis, Hospitalizations, and Death

The Center for Biologics Evaluation and Research (CBER) of the Food and Drug Administration (FDA) has suspended the biologics license for Ixchiq (chikungunya vaccine, live; Valneva, Saint-Herblain, France), citing serious safety concerns after postmarketing reports of chikungunya-like illness in vaccine recipients. The CBER determined that the vaccine poses an unacceptable risk, noting 21 hospitalizations, 3 deaths, and 1 confirmed fatal case of encephalitis linked to the vaccine strain.

Ixchiq was approved in November 2023 for the prevention of disease caused by infection with chikungunya virus. In May 2025, the FDA and Centers for Disease Control and Prevention (CDC) recommended to pause use of Ixchiq in adults aged ≥60 years to investigate reports of serious neurologic and cardiac events after administration. On August 6, 2025, the FDA lifted the pause in the use of Ixchiq after approving a label update to reflect the risk of hospitalization and encephalitis. The new decision, announced by the FDA on August 22, 2025, effectively halts the distribution and use of Ixchiq in the United States.

The FDA reported that serious adverse events following Ixchiq administration have included systemic illness resembling chikungunya disease and severe neurologic complications, including encephalitis. One individual who died due to encephalitis after receiving Ixchiq had confirmed presence of the vaccine strain of chikungunya virus in cerebrospinal fluid (CSF) polymerase chain reaction test results. In its statement, the FDA emphasized that confirmatory trials verifying the vaccine’s clinical benefit have not been completed, and overall, the benefit-risk profile no longer supports continued use of Ixchiq.