The Ixchiq chikungunya vaccine has caused serious side effects, especially in people aged 65 and older or with chronic conditions[1]. 28 cases of these effects have been reported[1]. Side effects resemble those of chikungunya infection and include fever, nausea, loss of appetite, and confusion, which can lead to falls[1]. Other symptoms are drowsiness, headache and rare cases of encephalitis[1]. The most common systemic effects in the studies were headache (32%), fatigue (29.4%) and myalgia (23.7%)[2]. Use of the vaccine in people over 65 has been temporarily restricted[1][3]. These effects can worsen existing diseases or general health[1].