DESCRIPTIVE EPIDEMIOLOGY OF ADVERSE EVENTS AFTER IMMUNIZATION - REPORTS TO THE VACCINE-ADVERSE-EVENT-REPORTING-SYSTEM (VAERS), 1991-1994

Objective: To provide an overview of the data, function, and performan ce of the Vaccine Adverse Event Reporting System. Design: Descriptive and correlational analyses. Setting: United States, 1991 through 1994. Subjects: Reports to the Vaccine Adverse Event Reporting System, a pa ssive national surveillance system, that represents temporal (but not necessarily causal) relationships between vaccinations and adverse eve nts. Main outcome measures: Demographic variables, birth weight, vacci ne type, severity of adverse event after immunization. Results: A tota l of 38,787 adverse events was reported during the study period withou t a clearly increasing or decreasing trend in the annual number of tot al reports or deaths. Of the deaths with known age, 72.4% were reporte d in the first year of life, and 63.7% of these were male. The peak ag e for death reports was 1 to 3 months, with a gradual decline through age 9 months, after which death was relatively rare. Adverse events wi th onset of symptoms the day of vaccination accounted for 45.5% of tot al reports; 20.4% had onset of symptoms the following day. Onset withi n 2 weeks after vaccination was noted for 92.5% of all reports. Simult aneous administration of multiple vaccines was noted in 75.7% of repor ts for immunizations at ages younger than 20 years. In contrast, among those 20 years or older, only 6.0% of reports named multiple vaccines . Wide geographic variations were noted in adverse event reporting rat es for children younger than 2 years, and the states with the lowest r eporting rates of less serious events included the most populous state s. Conclusions: The peak age of deaths at ages 1 to 3 months could be expected on the basis of prior studies showing that sudden infant deat h syndrome deaths peak at that age, that most deaths in the Vaccine Ad verse Event Reporting System are attributed to sudden infant death syn drome, and that sudden infant death syndrome has not been associated w ith vaccination. The large number of reports and national coverage of the Vaccine Adverse Events Reporting System make it useful for monitor ing the safety of vaccine lots and fbr accumulating case series to det ect or better understand adverse events that may occur too rarely to b e assessed in clinical trials or in the larger studies that are someti mes carried out by manufacturers after vaccine licensure (phase IV stu dies).