[Efficacy of influenza vaccination--the detection of a seeming efficacy]

In Japan, influenza vaccination has been offered to schoolchildren as a collective preventive program with parents given the right to participate or not participate in this program since 1987. Literature on the efficacy of influenza vaccination including the research report by the Ministry of Health and Welfare (1987) which proposed the continuation of the collective immunization program were examined. In almost all of the papers supportive of vaccination, approaches by which the final conclusions of the efficacy of vaccination were obtained have been found to be scientifically marginal in design and analysis. In order to further investigate these problems, a reanalysis of the data from recent studies by Satomi and Mori (1989) was conducted. A significant efficacy of the influenza vaccination could not be detected from this analysis, strongly suggesting that what appeared to be an efficacy in many papers may have been produced as a result of the confounding by the "healthiness" of the study population.