FDA monitors adverse event reporting rates for individual vaccine lots on the basis of crude estimates of lot size and the amount of time that the vaccine lot has been in distribution. The information available to the FDA includes VAERS data and manufacturers' reports, as described above. At weekly meetings, FDA personnel review all the data for lots for which a report of a serious adverse event (any event that requires hospitalization, results in permanent disability, is life threatening, or prolongs hospitalization) has been made during the past week. At these meetings the individual reports are discussed, as are the patterns of reporting, that is, the number of reports made during a specific time frame. Particular scrutiny is given to lots for which there have been relatively large numbers of adverse event reports early in their circulation.
At FDA, further investigation of lots with which adverse events have been associated includes a detailed review of individual reports to look for clusters of similar cases, syndromes that connect the reports, or other patterns. Additional information is sometimes collected from the reporter, primary physician, or medical examiner. The adverse event reporting patterns for other final lots filled from the same bulk vaccine are also considered. Of greater concern is if elevated adverse event reports are received for several final lots from the same batch bulk material than if the number of reports for one lot is higher and that for the others is lower. Lot release data are reviewed to ensure that the lots in question have passed all the required tests.
According to FDA representatives, reports of fatal events and reports of certain serious events are routinely followed up by FDA physicians or by VAERS personnel. Some consumer representatives, however, expressed discontent with the followup that they are aware of. Follow-up includes assessment of the current condition of the patient for nonfatal reports, confirmation of the information provided by the reporter, and requests for additional information, including a more detailed chronology of events and relevant facts about the child or family of the child who experienced the adverse event. Sometimes, additional laboratory results, hospital discharge summaries, or autopsy reports are requested. Sometimes the patient or family is contacted directly; at other times the medical records suffice. Reports of less serious events are occasionally investigated for unusual events or patterns.
Once the review process is complete, FDA has several options. The agency may determine that the vaccine lot in question is not likely to be faulty but will