Safety Alert Issued for Chikungunya Vaccine: Older Adults Advised to Pause Vaccination

A newly approved vaccine against the chikungunya virus, Ixchiq, developed by Valneva, is under scrutiny following reports of serious adverse events, including fatal complications, in older adults. The Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC) have jointly issued a safety notice recommending a pause in the use of the vaccine for individuals aged 60 and older, pending further evaluation of post-marketing safety data.

Ixchiq received FDA approval in November 2023, marking a significant milestone as the first vaccine available to prevent chikungunya, a mosquito-borne viral disease. The approval initially covered individuals aged 18 and older who are at risk of exposure to the virus, particularly travelers to regions where chikungunya is prevalent. The FDA had previously characterized chikungunya as an "emerging global health threat," highlighting the urgent need for effective preventative measures. Over the past 15 years, at least five million cases of chikungunya have been reported worldwide, underscoring the global burden of the disease.

However, recent reports of adverse events following vaccination have raised concerns about the safety of Ixchiq, particularly in the older adult population. The FDA and CDC’s safety notice, released on May 9, underscores the agencies’ commitment to monitoring the safety and efficacy of newly approved vaccines and responding promptly to emerging safety signals.

The decision to recommend a pause in vaccination for individuals over 60 was prompted by reports of serious adverse events, including neurologic and cardiac complications. Among the reported events, two cases resulted in death due to severe complications. One of the fatalities was attributed to encephalitis, an inflammation of the brain. The individuals who experienced these adverse effects ranged in age from 62 to 89, further emphasizing the potential risk to older adults.

The FDA and CDC are currently conducting a thorough evaluation of post-marketing safety reports to determine the underlying cause of the adverse events and assess the overall benefit-risk profile of Ixchiq in older adults. The agencies have assured the public that they will provide updates as soon as their evaluation is complete.

Ixchiq is a live-attenuated vaccine, meaning it contains a weakened version of the chikungunya virus. While this approach can effectively stimulate the immune system to produce protective antibodies, it also carries the potential risk of causing symptoms similar to those of the actual chikungunya infection. According to the CDC, typical symptoms of chikungunya include fever, severe joint pain, headache, muscle pain, and a rash. Most individuals recover within a week, but some may experience persistent and debilitating joint pain for weeks or months.

The FDA has cautioned that Ixchiq may cause symptoms resembling those of the chikungunya virus, which could pose a greater risk to older adults who may be more vulnerable to the adverse effects of the vaccine.

Chikungunya is caused by the chikungunya virus (CHIKV), which is transmitted to humans through the bites of infected mosquitoes, primarily Aedes aegypti and Aedes albopictus. These mosquitoes are also responsible for transmitting other viral diseases, such as dengue fever and Zika virus. Chikungunya is endemic in many parts of the world, including Africa, Asia, and the Americas. Travelers to these regions are at risk of contracting the virus.

The emergence and spread of chikungunya have raised concerns among public health officials worldwide. The virus can cause significant morbidity, particularly due to the debilitating joint pain that can persist for months or even years after the initial infection. This chronic pain can significantly impact an individual’s quality of life and ability to perform daily activities.

The FDA’s decision to approve Ixchiq was based on clinical trial data demonstrating the vaccine’s ability to elicit a robust immune response against the chikungunya virus. However, the post-marketing safety reports have raised concerns about the vaccine’s safety profile in older adults.

The FDA plans to conduct an updated benefit-risk assessment for Ixchiq use in individuals over 60 years of age. This assessment will consider the potential benefits of the vaccine in preventing chikungunya infection, as well as the risks of serious adverse events. The FDA will also evaluate the available data to determine whether specific risk factors may predispose older adults to adverse events following vaccination.

In the meantime, the FDA and CDC are urging healthcare providers to adhere to the recommendation to pause the use of Ixchiq in individuals aged 60 and older. They are also encouraging healthcare providers to report any adverse events that occur following vaccination with Ixchiq to the Vaccine Adverse Event Reporting System (VAERS).

The safety alert regarding Ixchiq highlights the importance of ongoing monitoring of vaccine safety after approval. Post-marketing surveillance plays a critical role in identifying rare but potentially serious adverse events that may not be detected during clinical trials. The FDA and CDC are committed to ensuring the safety and efficacy of vaccines and will continue to monitor the safety of Ixchiq and provide updates to the public as new information becomes available.