Pre-licensure trials are primarily designed to investigate efficacy, not safety. These trials are limited in their ability to provide data on delayed reactions or reactions in subpopulations.

PMID: 

Vaccine. 1999 Oct 29 ;17 Suppl 3:S41-6. PMID: 10559533

Abstract Title: 

Vaccine risks: real, perceived and unknown.

Abstract: 

As immunizations successfully reduce the incidence of their target diseases, the vaccine community needs to evolve and recognize the increased relative prominence of vaccine safety. Just as the aviation community maintained public confidence by its continuous investment in a safety infrastructure as it evolved from propeller to jet and jumbo planes, modernization of the vaccine safety infrastructure commensurate with the current investment in vaccine development will be needed if the full promise of new vaccines made possible by the biotechnology revolution are likely to be fulfilled.

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