Hypotonic-hyporesponsive episodes in children hospitalized at 10 Canadian Pediatric Tertiary-Care Centres, 1991-1994.

Hypotonic-hyporesponsive episode (HHE), sometimes called the ragdoll, collapse reaction, or shock-like state refers to an adverse event occurring after administration of whole-cell pertussis vaccine; the infant becomes pale and displays decreased responsiveness, muscle tone, and activity. Although HHE occurs most often after immunization with whole-cell pertussis vaccine, it has also been reported with lower frequency after diptheria-tetanus (DT) and acellular pertussis-DT vaccine. In a prospective study of 15,752 diptheria and tetanus toxoids, and pertussis (DPT) immunizations in the United States, the incidence of HHE was found to be 1 in 1,750 immunizations. Although HHE is often very disturbing to parents and physicians, long-term follow-up suggests that neurologic sequelae do not occur.