directly monitoring lots to see how well the predicted and actual number of doses in particular lots matched.

To better assess vaccine lot administration, a CDC representative suggested that vaccine manufacturers include postcards in some of the boxes of vaccines distributed. The cards would request that the provider, on the day that the box is opened and vaccine from that box is first given to a patient, write the date on the card and return it by mail. However, a manufacturer who had attempted such an approach believed that studies done in this manner do not generate reliable data because vaccine administration is extremely variable, making vaccine administration impossible to track through indirect methods such as this.

Improving the Usefulness of LLDB Data

The main problem with LLDB is that it is limited by how medical events are captured in their computer data systems during routine visits. It is difficult to discriminate between new events and chronic or recurrent conditions. For example, some databases do not distinguish among a visit for a first seizure, a visit for a recurrent seizure, or a follow-up or check-up visit. By using certain data screening techniques, however, it is possible to subcategorize visits. By limiting seizure reports only to those that occurred in the emergency room and that were separated by 30 days, for example, researchers were able to distinguish visits for actual seizure events from seizure follow-up visits or checkups (Davis, unpublished data). Such screening techniques might make the LLDB more useful, a vaccine researcher suggested.

An FDA representative suggested developing computerized screening methods to identify clusters of potentially related events. Researchers could also develop statistical methods that could more effectively evaluate adverse events following vaccination.

Clinical Trials

To further identify adverse reactions to vaccines, an FDA representative suggested that larger clinical trials of vaccines be performed before the vaccines are licensed for general use. Those studies would need to be large enough to detect rare serious adverse effects such as death or seizures. The speaker suggested the development of procedures for conducting such trials in an effective and efficient manner, noting that studies of this size have been done to evaluate agents used to reduce mortality following heart attacks.

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