I et studie hos ældre beboere i plejehjem, hvoraf 80% blev vaccineret i studieperioden, nedsatte 6 ugers behandling med oseltamivir, 75 mg en gang daglig, signifikant hyppigheden af klinisk influenza fra 12/ 272 (4, 4%) i placebogruppen til 1/ 276 (0, 4%) i oseltamivirgruppen (92% reduktion [95% konfidensinterval 1, 5 - 6, 6, p=0, 0015]).
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]).