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Oseltamivir once or twice daily safely prevented influenza

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 QUESTION: Is oral oseltamivir safe and effective in preventing naturally occurring influenza virus infection?


Two 6 week randomised (allocation concealed*), blinded (clinicians and patients),* placebo controlled trials during influenza season.


3 centres in Virginia, 2 in Texas, and 1 in Kansas, USA.


1562 people who were 18 to 65 years of age (mean age 35 y, 63% women) and were recruited by advertisement. Exclusion criteria were influenza vaccination in the previous year, meeting ≥1 criterion for influenza immunisation according to current (US) guidelines, acute respiratory illness with fever in the previous week, pregnancy, or potential for pregnancy. 1559 participants took ≥1 dose of the assigned study medication and were included in the analysis (intention to treat).


Participants were allocated to oral oseltamivir, 75 mg once (n=520) or twice (n=520) daily, or to placebo (n=519) for 6 weeks, beginning when influenza virus activity increased at the local study sites.

Main outcome measures

Laboratory confirmed influenza-like illness (laboratory confirmation was culture of influenza virus within 2 d of the onset of influenza symptoms or antibody titer on haemagglutination inhibition testing ≥4 times the baseline titer or both). Adverse events were also assessed.

Main results

Fewer patients receiving …

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  • Source of funding: Hoffmann-LaRoche.

  • For correspondence: Dr FG Hayden, Department of Medicine, Box 473, University of Virginia Health Sciences Center, Charlottesville, VA 22908, USA. Fax +1 804 924 9065.

  • * See glossary.