VAERS data have a number of limitations you should remember:
* VAERS data are derived from a passive surveillance system and
represent unverified reports of health events, both minor and serious,
that occur after vaccination.
* Such data are subject to limitations of under-reporting,
simultaneous administration of multiple vaccine antigens (making it
difficult to know to which of the vaccines, if any, the event might be
attributed), reporting bias, and lack of incidence rates in unvaccinated
comparison groups.
* While some events reported to VAERS are truly caused by vaccines,
others may be related to an underlying disease or condition, to drugs
being taken concurrently, or may occur by chance shortly after a vaccine
was administered.
http://www.vaers.org/info.htm