Potential of influenza vaccine and amantadine to prevent influenza A illness in Canadian forces personnel 1980-1983

Abstract

A randomized, placebo-controlled, single-blind trial was designed to compare the efficacy and side-effects of a standard influenza vaccine and amantadine chemoprophylaxis, to prevent influenza A virus illness in Canadian Forces Bases (CFB) personnel in Manitoba during three winter seasons from 1980-83. From 220 to 333 volunteers were allocated to vaccine (V), saline injection as vaccine placebo (VP), amantadine 100 mg/day (Al), 200 mg/day (A2) or placebo (AP) capsule groups. A median of 89% of V recipients had HAI titres <20, 4-6 weeks after immunization, indicating protection against illness due to vaccine strains. Myalgia was the commonest side effect but was not clinically important.

Influenza A community outbreaks due to vaccine strains, or antigenically related ones, occurred in 1980–81 and 1982–83. Chemoprophylaxis was continued for 32 and 39 consecutive days, respectively, during those periods and was well tolerated. However, 16% of Al or A2 recipients were noncompliant as evidenced by a lack of drug in urine or plasma. The incidences of laboratory-confirmed illness were 3 and 13 per 1000 in these two years, too low to enable us to assess the efficacy of our preventative measures. Subclinical influenza occurred in <10% of unimmunized subjects.

These data suggested that both strategies for preventing influenza in CFB personnel had the potential to be protective with minimal adverse effects. However, our data did not permit us to recommend one in preference to the other.