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candidates. Efficacy would be affected if recipients were unable to respond fully or to maintain immunity for a sufficient length of time.

Adverse Reactions

Adverse side effects of a vaccine, especially those likely to occur at very low frequency, are extremely difficult to predict but can seriously affect vaccine acceptance. Predictions about side effects are based on the nature of the new vaccine and its purity, and on observations of similar existing vaccines. To facilitate calculations, predictions concerning the incidence of adverse reactions are best expressed “per dose” rather than “per vaccinee.”

In this analysis, anticipated adverse reactions were judged, for the vaccines considered, to be negligible for the purposes of calculating potential vaccine benefits (see Chapter 7). For new contenders the likely reactions and their frequency should be evaluated to determine if an adjustment of the potential health benefits, which accounts for adverse reactions, is warranted.

Production Technology, Delivery Requirements, and Cost per Dose

The technical difficulty of producing a vaccine and the delivery (storage) requirements affect vaccine cost. The committee based its predictions in these areas on the nature of each vaccine candidate and on requirements for existing similar vaccines. Production technology and delivery requirements also affect the cost per dose, which, in turn, may affect vaccine acceptance.

Number of Doses and Route of Administration

The number of doses necessary to achieve a vaccine’s predicted protective efficacy and the route of administration also may affect the ease of integrating the vaccine into existing immunization programs. Predictions of these characteristics are based largely on the nature (including the probable antigenicity) of each vaccine candidate.


The predictions in Tables 5.1 and 5.2 resulted from extensive deliberations by the full committee on estimates made by a subgroup, with suggested revisions by many outside consultants. The predictions were designed to reflect relative differences in vaccine candidates’ prospects for development; they are not intended to be precise descriptions of future events. Predicting vaccine development is complicated by many factors, including the rapid pace of new advances in biotechnology. Some candidates excluded from the current analysis

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