Vaccine safety.

Rates of reported adverse events are remarkably low. VAERS identifies an adverse event rate approximating 11.4 reports per 100,000 vaccine doses. Approximately 15% of these reports represent SAEs, but less than 2% involve death; in most cases, reviews have shown no causal relation between the events and the vaccine. Across the spectrum of vaccines in use (including those directed against influenza and hepatitis B virus), many claims of adverse events regarding vaccines represent typical reactions to vaccinations. These reactions can be thought of as foreign-body reactions and predominate among the inactivated vaccines. In controlled studies, the adverse event rates that occur with vaccination resemble those that occur with placebo injections. Typical reactions associated with live viral and bacterial vaccines, such as MMR and varicella vaccines, may resemble attenuated forms of the disease for which the vaccine is directed. Other claims against vaccines represent chance-coincidence or misunderstood data; further studies of claims have vindicated the overall safety of the vaccines in most cases. Two documented safety concerns with vaccines, however, have demonstrated that vaccines (like other biologics and pharmacologic) can result in harm (eg, rotavirus and OPV vaccines). The denouement with these vaccines indicates the broad postmarketing data collection and evaluation that extends efforts made with prelicensure study to balance the benefits from vaccination with the risk for harm. Overall, measures including prelicensure study and postlicensure surveillance, such as VAERS, the Vaccine Safety Datalink Project, and the Clinical Immunization Safety Assessment Centers, have resulted in an exceptional safety profile for the vaccines in use.