Problems in the investigation of adverse reactions

All drugs and vaccines administered to man cause adverse reactions. In general the adverse reaction profile of a new vaccine should be defined in its clinical trial phase, but the incidence of adverse reactions occurring infrequently is likely to emerge only after extensive clinical use. Problems in the investigation and assessment of reports of adverse reactions which occur infrequently are reviewed. It is important that case reports be complete and include details of the batch number and manufacturer of the incriminated vaccine, and of its storage and administration. The assessment of reports of adverse reactions, which are similar in nature to those occurring in equivalent unvaccinated populations, presents special problems and may require case control studies. As new types of vaccines are developed it will be necessary to improve systems which monitor the occurrence of adverse reactions which occur infrequently and those which bear a distant time relationship to immunisation.