Comparison of military and civilian reporting rates for smallpox vaccine adverse events

Introduction US smallpox vaccination (SMA) started most recently in December 2002. Military and civilian personnel report adverse events (AEs) to the Vaccine Adverse Event Reporting System (VAERS), a surveillance system that relies on spontaneous reports. Although reported rates of probable myo/pericarditis after SMA in the literature are similar between military personnel and civilian healthcare workers, some civilian AE reporting rates after SMA appeared higher than those in the military. Objective Determine if SMA-associated reporting rates are different in civilians than in the military, considering age, sex, seriousness, and expectedness of the AE, as well as self-reporting. Methods Numerators were SMA reports in VAERS from 12/12/02 to 3/1/04. Limitations of VAERS include underreporting and lack of diagnostic confirmation. Denominators were number of military and civilian vaccinees. Results Reporting rates stratified by age and sex of serious and non-serious AEs were significantly higher in civilian than military personnel ages <55 years (rate ratios 4-27). These rate ratios decreased with increasing age. Conclusions Reporting rates in VAERS differed significantly and substantially in civilians compared to military personnel <55 years of age. Differences in stimulated passive surveillance systems, and AE reporting practices, including the 'threshold' for reporting most likely explain these findings. These results suggest that in the case of smallpox vaccine AEs, there may be systematic differences in reporting completeness between the civilian and military sectors, and that passive surveillance data should be interpreted with caution. Copyright (C) 2006 John Wiley & Sons, Ltd.