A hypotonic-hyporesponsive episode (HHE) is the sudden onset of muscle limpness, reduced responsiveness or unresponsiveness, and pallor or cyanosis occurring after vaccination in early childhood. The episode usually occurs within 48 hours of vaccination and resolves spontaneously without treatment. Our new reference page describes HHE, its incidence and its impact on future vaccination.

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MVEC: Hypotonic-hyporesponsive episode (HHE)