Introduction:

The hypotonic-hyporesponsive episode (HHE) is defined by the sudden decrease in muscle tone, hyporesponsiveness, and skin discoloration (pallor or cyanosis), which may begin immediately or within 48 hours after immunization, where no other cause is known.

Case report:

The authors describe a case of a lactent, referred to the allergy and clinical immunology department due to an anaphylaxis suspicion post-vaccination in which the allergological workout excluded this diagnosis, proved tolerance to the pentavalent vaccine, and confirmed the HHE diagnosis.

Comment:

This case reinforces the importance of sending these children to an allergy clinic, to perform a correct diagnosis and confirm/exclude a vaccine allergy. HHE is rare, not very often described in the literature, and can occur in any children vaccinated. It should not be considered a contraindication for future immunizations, but the vaccination after the episode should be carried in a hospital setting, under supervision.

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