The time to licensure is defined as the earliest time that a vaccine could be licensed if all developmental stages are completed without major delays. Factors considered in determining this time were similar to those used to estimate the cost of development.

The committee also considered interrelationships between the probability of success, the cost of development, and the time to licensure, for example, the extent to which extra funding could significantly reduce the time to licensure for a particular vaccine.

The committee based predictions on the characteristics of individual vaccines primarily on known characteristics of existing vaccines of similar type, e.g., live attenuated virus, polysaccharide, or subunit vaccine. These predictions also incorporate assumptions about likely licensure requirements.

The prediction of a vaccine’s efficacy represents a population-based measure of protection* rather than a measure of antibody production in an individual. Factors considered in estimating the efficacy were the type of pathogen and number of serotypes involved in the disease, the nature of the vaccine candidate, and the extent of immunity from natural infection.

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