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Fetal perspective of rubella vaccine efficacy and safety.

Licensure of a new vaccine requires a judgment concerning efficacy and safety that, in most cases, have been demonstrated by "clinical" trials conducted in previously nonimmune volunteers. Evidence for efficacy is provided by demonstration of relevant antibody response by a high proportion (at least 95%) of vacinees and of significant protection against challenge (disease or infection prevented). Observations as to the frequency and nature of adverse effects induced in vaccine recipients constitute the evidence relating to safety. The point is not how efficacy and safety are defined but that the relevant evidence for both ordinarily comes from direct observation of the persons who receive the vaccine. Rubella vaccine differs from other vaccines in that the principal intended beneficiaries will be fetuses not yet conceived. Thus, while it was necessary that efficacy and safety for vaccinees be demonstrated (and they have been), much more evidence is required before well-founded judgments can