Postlicensure

Rates within the vaccinated population can be compared to rates in a control group in prelicensure studies or to rates of events outside the specified time window in postlicensure evaluations.

Because of concerns about intussusception identified in prelicensure trials, VAERS data were analyzed early in the postlicensure period.

The well-known limitations associated with prelicensure trials have led to the expectation that postlicensure studies would address safety issues better.

Postlicensure vaccine safety monitoring is now a multifaceted activity which helps address these concerns as well.

However, recent postlicensure data from international settings suggest the possibility of a low level elevated risk, primarily in the first week after the first vaccine dose.