nated so far. Therefore, the consistent use of the Active Surveillance System would provide a rich source of data for detecting trends in reported adverse events.

In its first letter report (IOM, 2003b), the committee identified its reasons for recommending the creation and use of an active surveillance system:

Considering the anticipated risks of the vaccination program and the currently unknown benefit, it is extremely important that all adverse reactions from the smallpox vaccine (both known and suspected) be identified in a timely manner. Relying on passive systems that are dependent on vaccinees and their clinicians to bring the adverse reaction to the attention of the smallpox vaccination program managers will not capture all serious adverse reactions.

The committee still believes in the value of the Active Surveillance System but recognizes the importance of doing an evaluation of the efficacy of the system so its role in the ongoing program can be assessed. Such an evaluation should involve getting data on every person vaccinated in the first phase of the program entered into the Active Surveillance System, and then evaluating the completeness, validity, and added value of the data gathered through the Active Surveillance System compared to other means (e.g., VAERS, the Clinician Information Line). Once such an evaluation is conducted (with as complete ascertainment as possible of data on all vaccinees, so reliable statistical analyses can be generated), the committee and CDC can have a better understanding of the relative value of the Active Surveillance System in the ongoing operation of the pre-event smallpox vaccination program. Regardless, such an evaluation would provide reassurance of the completeness of safety data, and correspondingly, the overall safety of the vaccination program.

It is important to recognize, however, that an evaluation of the Active Surveillance System during the first phase of the program may not necessarily be generalizable to the expanded program. In the expanded vaccination program, there may be a larger number of people vaccinated than in the first phase of the program. Because of this potentially larger number of vaccinees, there may also be a larger number of adverse events reported. The standardized data collection format used in the Active Surveillance System may make investigations easier for this potentially greater volume of reported adverse events and may allow determinations of probable causality to be made more quickly, potentially lessening the sense of alarm that would arise from the sheer volume of adverse events that could be reported. In addition, whereas the first phase of the program focused on public health and health care workers who already may have had knowledge of adverse event reporting mechanisms, workers vaccinated in the expanded vaccination program (and their fellow workers who may be entering data on this



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