CDC investigating hospitalizations of five people who recently received chikungunya vaccine

CNN

27-02-2025

The US Centers for Disease Control and Prevention is currently investigating five hospitalizations that occurred in people who had recently received a vaccine that prevents disease caused by the chikungunya virus.
In a notice posted Tuesday on a vaccine information page for health-care providers, the CDC said that the people, all 65 and older, were hospitalized for cardiac or neurologic events following vaccination with IXCHIQ, the only chikungunya vaccine currently licensed in the United States.
CNN has reached out to the CDC for comment.
Chikungunya virus is typically spread to people through the bite of an infected mosquito. Most adults don't receive the vaccine; it is sometimes recommended for certain travelers at an increased risk of being exposed to the mosquito-borne disease.
'This topic will be discussed at an upcoming meeting of the Advisory Committee on Immunization Practices (ACIP). Healthcare providers should discuss the benefits and risks of vaccination with individual travelers based on their age, destination, trip duration, and planned activities,' the CDC's online notice said in part.
The chikungunya vaccine and surveillance for adverse events originally were scheduled to be discussed in an ACIP meeting Wednesday, according to a draft meeting agenda, but that meeting has been postponed.
Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical Center and ACIP liaison, said the CDC investigation is an example of the agency's vaccine surveillance system 'working excellently and sending out a signal' in detecting rare events that might deserve further investigation.
'And of course, the CDC and the local people who are taking care of these patients are working on that now, which is entirely appropriate. That's the way the system is supposed to work,' Schaffner said.
'Remember, we're still trying to work out whether this is a causal relationship or a coincidental one,' he said about the investigation, in which he is not directly involved. 'Let's not draw any conclusions yet. That's why they're doing the investigation.'
The IXCHIQ vaccine, administered as a single-dose shot into the muscle, contains a live, weakened version of the chikungunya virus. The vaccine, manufactured by the biotechnology company Valneva, was the first vaccine approved by the US Food and Drug Administration to prevent disease caused by chikungunya virus. The approval, in November 2023, was for people 18 and older who are at increased risk of exposure to chikungunya virus.
'It's recommended in a very restricted way to travelers who are going to countries where there is a current outbreak of chikungunya virus infection, and also to travelers who are going to countries who had experienced an outbreak within the past five years,' Schaffner said. 'And also to laboratorians who work with the chikungunya virus in the laboratory.'
CNN has reached out to Valneva for comment. Prescribing information for the vaccine states, 'Vaccination with IXCHIQ may cause severe or prolonged chikungunya-like adverse reactions.'
Chikungunya virus circulates in tropical and subtropical regions. In the United States, locally acquired infections have not been reported since 2019, according to the CDC. But cases and outbreaks had been identified in more than 100 countries in the Americas, Africa, Asia, Europe, and the Indian and Pacific Oceans.
Symptoms of chikungunya infections include fever, joint pain, headache, muscle pain, joint swelling or rash, according to the CDC, and the best way to prevent chikungunya is to avoid mosquito bites. There are currently no medications to treat chikungunya, but infected people may feel better with rest, fluids and over-the-counter medications for pain and fever.
In Tuesday's notice, the CDC said that common adverse reactions following vaccination that occurred in more than 10% of vaccinated people in clinical trials included tenderness, headache, fatigue, muscle pain, joint pain, fever and nausea. In some people, 'severe or prolonged chikungunya-like adverse reactions' occurred.
Chikungunya-like reactions included 'fever, joint pain, headache, rash, and can also include cardiac and neurologic conditions which were serious in two cases,' Dr. Dan Barouch, director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center, who was not involved in the clinical studies, said in an email Wednesday.
The CDC's notice encouraged health-care providers 'to report all adverse events that might be caused by vaccination to the CDC/FDA Vaccine Adverse Events Reporting System (VAERS),' by submitting a report online or using a PDF form.
'The robust vaccine safety surveillance system often identifies extremely rare adverse effects of vaccines after approval,' said Barouch, an infectious disease expert not involved in the CDC investigation.
When the vaccine was approved in 2023, the FDA noted that its safety was evaluated in two clinical studies conducted in North America in which about 3,500 adults received a dose of the vaccine, with one study including about 1,000 participants who received a placebo. Severe chikungunya-like adverse reactions occurred in 1.6% of IXCHIQ recipients and none of the placebo recipients, according to the FDA.