A study in elderly residents of nursing homes, where 80% of participants received vaccine in the season of the study, oseltamivir 75 mg once daily given for 6 weeks significantly reduced the incidence of clinical influenza illness from 12/ 272 (4.4%) in the placebo group to 1/ 276 (0.4%) in the oseltamivir group (92% reduction [95% CI 1.5 – 6.6; p = 0.0015]).