The FDA has suspended approval for the chikungunya vaccine Ixchiq, citing “serious safety concerns.”

Chikungunya is a mosquito-borne viral disease caused by the chikungunya virus. It has been detected in more than 100 countries in Asia, Africa, Europe and South America. From January through July, there were some 240,000 cases and 90 deaths, according to the European Centre for Disease Prevention and Control. 

The CDC generally recommends precautions, such as vaccination, for travelers to areas at higher risk for chikungunya.

The FDA said in a statement that it had determined that one of the two approved vaccines, Ixchiq (Valneva SE), which contains a live, weakened version of the chikungunya virus, was responsible for 21 hospitalizations and three deaths.

Ixchiq is known to cause chikungunya-like symptoms. Fever, headache, myalgia and other chikungunya-type symptoms were observed in clinical trials and a warning about such symptoms was included in the label when the FDA approved Ixchiq in November 2023.

At a meeting of the CDC’s Advisory Committee on Immunization Practices (ACIP) in April, a CDC official said the FDA first began receiving adverse event reports related to Ixchiq in 2024. The most serious adverse events were in recipients in their late 60s to late 80s who had underlying cardiovascular disease and other chronic conditions. 

Soon after the ACIP meeting, the FDA announced it was recommending a pause in Ixchiq vaccination for individuals aged 60 or older while the agency further investigated the reported events. At the time, the FDA said there were 17 events, including two deaths, reported globally. Also at that time 80,000 doses had been distributed worldwide.

The agency lifted the pause in early August but recommended that the label be updated to reflect that it should only be given to people at “high” risk for exposure, and that serious reactions had been reported in the postmarketing period. 

Now the FDA said it believes Ixchiq “is not safe and that continued administration to the public would pose a danger to health.”

Valneva said in a statement that it would continue marketing Ixchiq outside the US, and that the serious adverse events reported were similar to what had been observed during trials. The company “is continuing to investigate these cases in detail and if warranted will pursue further steps in connection with FDA’s decision in accordance with applicable statutory procedures,” the company said.

Another chikungunya vaccine, Vimkunya (Bavarian Nordic), is still available. The FDA approved the recombinant virus-like particle-based vaccine in February. In April, the ACIP recommended Vimkunya for individuals aged 12 years or older who are traveling to a country or territory where there is a chikungunya outbreak.

Alicia Ault is a Saint Petersburg, Florida-based freelance journalist whose work has appeared in many health and science publications, including Smithsonian.com. You can find her on X @aliciaault and on Bluesky @aliciaault.bsky.social.