United States: The US Centers for Disease Control and Prevention (CDC) has launched an inquiry into five hospitalizations involving individuals who had recently been administered the IXCHIQ vaccine, which offers protection against the chikungunya virus.
In a notification published Tuesday on a vaccine information portal for healthcare providers, the CDC disclosed that all five individuals, aged 65 and older, were admitted to hospitals due to cardiac or neurological incidents following vaccination with IXCHIQ—the sole chikungunya vaccine currently sanctioned in the United States.
The chikungunya virus is predominantly transmitted through the bite of an infected mosquito. While the vaccine is not routinely administered to the general adult population, it is occasionally advised for particular travelers who might face an elevated risk of encountering this mosquito-borne illness, according to the reports by CNN.
The CDC’s announcement noted, “This matter will be addressed at an upcoming session of the Advisory Committee on Immunization Practices (ACIP). Healthcare professionals should engage in discussions with individual travelers about the potential advantages and risks of vaccination, considering factors such as age, destination, trip duration, and planned activities.”
Though originally slated for discussion during an ACIP meeting on Wednesday, as indicated by a draft agenda, the session has been postponed.
Dr. William Schaffner, an infectious disease specialist at Vanderbilt University Medical Center and a liaison to the ACIP, described the CDC’s investigation as a testament to the efficacy of the agency’s vaccine monitoring framework. He emphasized that the system’s ability to detect rare events warranting further scrutiny exemplifies its intended purpose.
“At present, local healthcare providers and the CDC are diligently examining this situation, which is precisely how the process is designed to function,” Schaffner said.
He cautioned against premature conclusions, stating, “We are still working to determine whether this represents a causal link or merely a coincidence. The investigation is ongoing for precisely this reason.”
The IXCHIQ vaccine is administered as a single-dose intramuscular shot and contains a live, attenuated strain of the chikungunya virus. Produced by the biotechnology firm Valneva, it became the first vaccine approved by the US Food and Drug Administration (FDA) in November 2023 to prevent chikungunya virus infections. The vaccine is authorized for use in adults 18 and older who are at heightened risk of exposure to the virus.
“It is recommended selectively for travelers heading to regions experiencing an active chikungunya outbreak, as well as those traveling to areas that have witnessed an outbreak within the last five years,” Schaffner explained. “Additionally, it is advised for laboratory personnel who handle the chikungunya virus,” according to the reports by CNN.
A representative for Valneva acknowledged the CDC’s review of post-marketing safety data as part of routine vaccine oversight in a Thursday morning email.
The statement highlighted that at least four of the five affected individuals had received other vaccines, and most had significant pre-existing medical conditions. According to Valneva, their monitoring has not revealed any safety concerns, with the vaccine’s safety profile aligning with clinical trial data.
“No alterations have been observed in the established clinical trial safety profile, which encompasses over three years of post-vaccination monitoring,” the statement read. “Valneva remains committed to collaborating with health authorities to uphold the highest standards of vaccine safety.”
The vaccine’s prescribing information includes a warning: “Vaccination with IXCHIQ may provoke severe or prolonged chikungunya-like adverse reactions.”
Chikungunya virus thrives in tropical and subtropical climates. While the CDC reports that no locally acquired cases have occurred in the US since 2019, outbreaks have been documented in over 100 nations across the Americas, Africa, Asia, Europe, and the Indian and Pacific Oceans.
Infected individuals typically experience fever, joint pain, headaches, muscle pain, joint swelling, or rash, according to the CDC. Prevention primarily involves avoiding mosquito bites, as there are no specific treatments for chikungunya. Supportive care, such as rest, hydration, and over-the-counter medications for pain and fever, may alleviate symptoms.
In its Tuesday notice, the CDC noted that in clinical trials, common adverse reactions reported by more than 10 percent of vaccinated participants included tenderness, headaches, fatigue, muscle pain, joint pain, fever, and nausea. In some instances, “severe or prolonged chikungunya-like adverse reactions” were observed.
These reactions encompassed symptoms like fever, joint pain, headaches, and rash, and in two cases, serious cardiac and neurological conditions emerged, according to Dr. Dan Barouch, director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center. Barouch was not involved in the clinical trials.
The CDC has encouraged healthcare providers to report all potential vaccine-related adverse events to the CDC/FDA Vaccine Adverse Events Reporting System (VAERS), utilizing either an online platform or a PDF form, according to the reports by CNN.
Barouch emphasized the robustness of the vaccine safety surveillance system, noting its capacity to detect extremely rare adverse effects following vaccine approval.
When IXCHIQ was authorized in 2023, the FDA underscored that its safety had been thoroughly evaluated in two clinical trials in North America. Approximately 3,500 adults received the vaccine in these studies, including around 1,000 participants who were administered a placebo. According to the FDA, severe chikungunya-like adverse reactions were reported in 1.6% of IXCHIQ recipients, with no such reactions occurring in the placebo group.
