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May 23, 2025
The European Medicines Agency (EMA) has recommended restricting the use of the world’s first chikungunya vaccine, Ixchiq, in people over the age of 65 after reports of serious adverse events, including two deaths, among elderly recipients. The decision comes as experts raise concerns about the underrepresentation of older adults in clinical trials, highlighting a longstanding issue in medical research.
Serious Adverse Events Prompt Caution
Chikungunya is a mosquito-borne disease prevalent in tropical regions, known for causing severe and sometimes long-lasting joint pain. The Ixchiq vaccine, developed by Valneva, uses a genetically modified, weakened version of the chikungunya virus to stimulate immunity. Since its approval by the EMA a year ago, more than 40,000 people worldwide have received the vaccine, including 19,000 in the United States and 12,000 in France.
However, at least 17 serious adverse events have been reported in people over 62 who received the vaccine, with two cases proving fatal. One victim, an 84-year-old man, developed encephalitis—a rare but severe complication—while another, a 77-year-old man with Parkinson’s disease, also died after vaccination. Investigations are ongoing, but the EMA noted that the vaccine strain was detected in bodily fluids of both individuals.
Underrepresentation in Clinical Trials
The EMA’s initial review found that only 7.5% of clinical trial participants were over 65, compared to the nearly 20% this age group represents in the European Union population. While no major safety concerns were initially identified, the recent incidents have prompted the EMA’s Pharmacovigilance Committee to temporarily contraindicate the vaccine for those aged 65 and older. The U.S. Food and Drug Administration (FDA) has taken a similar step, lowering the age limit to 60.
Experts like Rosa López Gigosos of the Spanish Association of Vaccinology suggest these adverse events may represent previously undetected risks in older adults. She notes that vaccines using live attenuated viruses, such as Ixchiq, typically cause more side effects than those using only parts of the virus, and are often not recommended for the elderly or those with underlying health conditions.
A Broader Issue in Medical Research
The controversy has reignited debate over the lack of diversity in clinical trials—a problem that affects not only the elderly but also women, ethnic minorities, and people with certain health conditions or from rural areas. According to Alberto Borobia, head of the Clinical Research and Clinical Trials Unit at La Paz Hospital in Madrid, drugs may not have the same safety and efficacy in underrepresented groups as observed in trials.
Efforts are underway to address this gap. The READI project, led by La Paz Hospital and involving 73 organizations across 18 countries, aims to improve inclusion of diverse populations in clinical research. Meanwhile, a second chikungunya vaccine based on protein technology, Vimkunya, was approved by the EMA three months ago and may offer a safer alternative for older adults.
Looking Ahead
The European Commission has requested a formal opinion from the EMA on the future use of Ixchiq in older adults by September 30, 2025. In the meantime, health authorities in several countries have paused or restricted vaccination campaigns targeting seniors.
As the medical community continues to learn from these incidents, experts stress the importance of designing clinical trials that better reflect the diversity of the populations they aim to protect.
Disclaimer:
This article is based on information available as of May 23, 2025, and summarizes findings from the European Medicines Agency and reporting by EL PAÍS. The investigation into the adverse events linked to the chikungunya vaccine is ongoing, and a definitive causal relationship has not yet been established. Individuals should consult healthcare professionals for personalized medical advice.
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