Episode of hypotonia–hyporesponsiveness following immunization with an acellular pertussis–containing combination vaccine

Post-vaccination Hypotonic-Hyporesponsive Episodes (HHE) are characterized by a sudden loss of muscle tone associated with reduced responsiveness to stimuli, skin pallor or cyanosis. This adverse event is mainly described following pertussis vaccination, with a significantly lower risk with the acellular vaccine compared to the whole-cell vaccine. We report the case of an infant who following administration of the 2-month vaccines, presented with an unresponsive episode consistent with post-vaccination HHE event, with subsequent favorable clinical evolution. We emphasise the importance of early recognition of this adverse event, as well as its management and considerations regarding the administration of subsequent vaccine doses.