The Pharmacovigilance Risk Assessment Committee (PRAC) warns of the risk of aseptic meningitis associated with the Ixchiq chikungunya vaccine[1][2]. The Ixchiq vaccine is a live attenuated vaccine containing the ECSA/IOL genotype CHIKV Δ5nsP3 strain, indicated for persons 12 years of age and older for the prevention of chikungunya[1][2][3]. PRAC reported a case of fatal encephalitis and another case of aseptic meningitis where PCR testing and sequencing confirmed the presence of the vaccine strain in blood and cerebrospinal fluid[1][2]. These cases raised the question of insufficient attenuation or reversion of virulence, but the PRAC concluded that the risk of reversion was low given the genetic stability of the attenuation method[1][2]. The PRAC recommends updating the product information for the risks of encephalitis, encephalopathy, aseptic meningitis, confusional state, syncope, thrombocytopenia, malaise and decreased appetite[1][2]. Ixchiq recommends that the vaccine be given only when there is a significant risk of chikungunya infection after weighing the risks and benefits, especially in people with chronic diseases[1][2]. In clinical trials, the vaccine induced a reliable immune response that was sustained for 6 months in 99% of vaccinated adults versus 0% in the placebo group[3].