Objective: To describe the individual characteristics, clinical features, and morbidity associated with syncope following immunization.
Design: Large case series.
Setting: United States, 1990 through 1995.
Subjects: Reports to the national Vaccine Adverse Event Reporting System (VAERS), a passive surveillance system. An additional 3 reports of head injury (documented by medical records) were obtained through the National Vaccine Injury Compensation Program.
Main outcome measures: Syncope, syncope and hospitalization, or syncope and head injury within 12 hours of vaccination.
Results: A total of 697 cases of syncope after vaccination was reported. Age younger than 20 years was reported for 77.4%; 57.5% were female. Hospitalization was reported in 9.6%. Of the 571 syncope events with known time, 511 occurred 1 hour or less after vaccination. Of these, 323 (63.2%) occurred 5 minutes or less, 454 (88.8%) occurred 15 minutes or less, and 500 (97.8%) occurred 30 minutes or less after vaccination. Tonic or clonic movements, which have been associated with the anoxia of vasovagal syncope, were reported in 30.4% of syncopal episodes occurring 15 minutes or less after and in 12.8% of those occurring 15 minutes or longer after vaccination (P < .001). Six patients suffered skull fracture, cerebral bleeding, or cerebral contusion after falls; 3 of these patients required neurosurgery. Falls occurred 15 minutes or less after vaccination, in or near the clinic or office. Ages ranged from 12 to 28 years; 5 of 6 were male. Follow-up revealed substantial residual impairment in 2 patients.
Conclusions: Prevention of injury from syncope after vaccination and of syncope itself may be possible in many cases. Vaccinators should be aware that patients exhibiting presyncopal signs and symptoms around the time of immunization need to be evaluated carefully and may need to be assisted to sit or lie down after immunization until free of symptoms.