Low‐dose oral interferon alpha as prophylaxis against viral respiratory illness: a double‐blind, parallel controlled trial during an influenza pandemic year

BACKGROUND AND OBJECTIVE: Interferon alpha (IFNα) is a known antiviral agent. A double‐blind, placebo‐controlled clinical trial was conducted investigating the use of low‐dose oral interferon alpha for preventing acute viral respiratory illnesses. METHODS: Two hundred healthy adults aged 18–75 years were enrolled and completed weekly health data questionnaires to monitor for symptoms and impact of respiratory illness. Serum samples were tested for antibodies against influenza and other common respiratory viruses. RESULTS: Low‐dose oral IFNα prophylaxis did not reduce the incidence or impact of acute respiratory illness (ARI) or the impact of illness on daily activities. Post hoc analysis of participant subgroups, however, identified significant reductions in the incidence of ARI reported by males, those aged 50 years or more and those who received the 2009 seasonal influenza vaccine. Interferon alpha prophylaxis had a significant impact on the reporting of moderate‐to‐severe feverishness by the study population. Seropositive participants in the IFN group were more likely to report asymptomatic or mild symptoms compared with those in the placebo group who were more likely to report stronger symptoms. CONCLUSIONS: Low‐dose oral IFNα prophylaxis was not effective in limiting the overall incidence of ARI in our study population. However, there was evidence that prophylaxis reduced the severity of symptoms and had a beneficial effect in some subpopulations, including those who received the 2009 seasonal trivalent influenza vaccination.