Credible estimates of vaccine adverse reaction under-reporting

Connaught testimony to the Institute of Medicine

James Froeschle, Connaught Laboratories, Swiftwater, Pennsylvania Dr. Froeschle gave information about adverse events following diphtheria and tetanus toxoids (DT) that had been reported to Connaught.  From a comparison of spontaneous reports with postmarketing surveillance data, the company estimates about a 50-fold underreporting of adverse events in the passive reporting system.  The distribution of types of events, however, was found to be approximately the same; in both cases, the majority of reported events were local reactions or fever.  The company has seen a marked decrease in adverse event reports since the inception of VAERS late in 1991, because physicians are now requested to send reports directly to the VAERS contractor.

David Kessler statement in JAMA - June 2, 1993,vol.269, No.21, p.2785

Although the FDA receives many adverse event reports, these probably represent only a fraction of the serious adverse events encountered by providers.  A recent review article found that between 3% and 11% of hospital admissions could be attributed to adverse drug reactions.  Only about 1% of serious events are reported to the FDA, according to one study.