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The following is part of "Tips From Other Journals" from the October 1, 1997 edition of American Family Physician.

Characteristics of Syncope Occurring After Vaccinations

Vasovagal reaction is a commonly occurring syndrome that is caused by hyperstimulation of the sympathetic nervous system in response to pain, fear or emotional distress. The hyperstimulation is followed by a sudden onset of hypotension that often results in syncope. Syncopal seizures may also develop secondary to transient cerebral anoxia. Vasovagal fainting may occur in association with the administration of vaccines, although the clinical characteristics of these episodes and the propensity for secondary physical injury have not been well defined. Braun and associates evaluated all cases of vaccine-related syncope that were reported to the Vaccine Adverse Event Reporting System (VAERS) from 1990 through 1995.

During this five-year period, a total of 697 patients were reported to VAERS as having experienced syncope within 12 hours following vaccinations. Of the 615 patients for whom age was reported, 279 (45.4 percent) were between 10 and 19 years of age. A total of 197 children (32.0 percent) were younger than 10 years of age, and the peak frequency occurred in children four to six years of age. Of the patients for whom data on sex were noted (628), 57.5 percent were female; there was an excess of females in all age groups, except for those less than one year of age. The specific amount of time that elapsed between the vaccination and the syncopal episode was available in 571 reports. Of these episodes, 323 (63.2 percent) occurred within five minutes or less, 454 (88.8 percent) occurred within 15 minutes or less, and 500 (97.8 percent) occurred within 30 minutes or less following vaccination.

Six patients experienced syncope-induced falls that resulted in serious head injury, including skull fracture, cerebral bleeding and cerebral contusion. All six patients experienced the episode within 15 minutes of vaccination and were injured either in or just outside the office or clinic where the vaccination was given. Three of these patients required surgery, and two were left with substantial residual deficit at six months to two years after follow-up.

The authors conclude that syncope following immunization is common and that the true number of incidents is likely underreported. At least one immunization is recommended in the United States for every 10-year age group, which theoretically places the entire population at risk. While the causes of syncope may be heterogenous, the timing, description and clinical course suggest that most reported cases were caused by vasovagal reaction. During the time of this study, VAERS also received 168 reports of anaphylaxis and 3,121 reports of seizures following vaccinations. Approximately 25 percent of patients who experienced syncope also had tonic or clonic movements. However, after further diagnostic evaluations, none of these patients were found to have a new seizure disorder. Anaphylaxis could have caused some of the syncopal episodes, but in the absence of tachycardia, itching, urticaria or wheezing, this would be unusual.

The authors believe that prevention of injury from syncope following immunizations is feasible. Some episodes may be prevented if health care providers recognize presyncopal signs and symptoms, such as pallor, perspiration, trembling, bradycardia or hypotension. Patients with these signs and symptoms may need to sit or lie down for 10 to 15 minutes before and immediately after immunizations are given. Physicians may want to consider instituting a time policy as well as a designated waiting area that is monitored in the event of a syncope-related fall.--Jeffrey T. Kirchner, D.O.

Braun MM, et al. Syncope after immunization. Arch Pediatr Adolesc Med 1997;151:255-9.

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