Long-term use of oseltamivir for the prophylaxis of influenza in a vaccinated frail older population

OBJECTIVES: To investigate the efficacy of once-daily oral oseltamivir for 6 weeks (Tamiflu (TM)) in prophylaxis against laboratory-confirmed clinical influenza in frail older subjects living in homes for seniors and to deter mine the safety and tolerability of long-term oseltamivir. DESIGN: Double-blind, placebo-controlled, parallel-group, randomized, multi center study. SETTING: Thirty-one residential homes for seniors across United States and Europe. PARTICIPANTS: Five hundred forty-eight frail older occupants (mean age 81 y ears, > 80% vaccinated). INTERVENTION: Prophylaxis with oseltamivir 75 mg or placebo once daily for 6 weeks, beginning when influenza was detected locally. MEASUREMENTS: The primary efficacy endpoint was laboratory-confirmed clinic al influenza. RESULTS: Oseltamivir administration resulted in a 92% reduction in the inci dence of laboratory-confirmed clinical influenza compared with placebo (pla cebo 12/272 (4.4%), oseltamivir 1/276 (0.4%); P = .002). Of subjects vaccin ated against influenza, oseltamivir was 91 % effective in preventing labora tory-confirmed clinical influenza (placebo 11/218 (5.0%), oseltamivir 1/222 (0.5%); P = .003). Oseltamivir use was associated with a significant reduc tion in the incidence of secondary complications (placebo 7/272 (2.6 %), os eltamivir 1/276 (0.4%); P = .037). Although nearly all subjects were taking concomitant medication both before and during the study, oseltamivir was w ell tolerated. A similar incidence of adverse events, including gastrointes tinal effects, occurred in both groups. There was no suppression of antibod y response in oseltamivir recipients. CONCLUSION: Oral oseltamivir 75 mg once daily for 6 weeks effectively preve nted clinical influenza in vaccinated frail older subjects using significan t concomitant medications in a residential care setting. The treatment was well tolerated and provided additional protection to that afforded by vacci nation.