Potter J, Stott DJ, Roberts MA, et al. Intervention 6 hospitals were allocated to a vaccination program where HCWs were vaccinated, and 6 hospitals were allocated to a no-vaccination program. 1078 HCWs were involved in the study.
Main outcome measures Patient mortality and occurrence of influenza-like illness.
P value calculated from data in article. If you think the epidemiology of influenza has been fully described, think again. Potter and colleagues have provided some very interesting and important new findings. Vaccination of some HCWs and not others in the same institution would have resulted in partial herd immunity and confounded the determination of communicability. This study was not designed to show vaccine efficacy in the patients themselves and did not have the statistical power to do so.