Effect of Rimantadine on Induced Specific Serum Haemagglutination-Inhibiting Antibody and Nasal IgA Titres after Experimental Exposure of Adults to Influenza a Virus

Haemagglutination-inhibiting (HI) antibody and specific nasal IgA responses to infection with influenza A (H1N1) virus were compared between 35 rimantadine-treated subjects (100 mg, orally, twice daily from day 2 to day 10, post-challenge) and 36 placebo-treated subjects. Infection was documented in 29 (83%) and 34 (94%), viral shedding in 24 (69%) and 30 (83%), and seroconversion in 21 (60%) and 27 (75%) of the rimantadine- and placebo-treated subjects, respectively. The duration of virus shedding (1.7±1.6 days compared with 3.1±2.1 days) was significantly lower in the rimantadine-treated group. Both groups had significant increases in the HI (21 days post-challenge) and virus-specific nasal IgA antibody (7 days post-challenge) titres. Convalescent HI but not IgA antibody titre was significantly greater in the placebo group. Convalescent HI antibody titre correlated with virus shedding, suggesting that differences between treatment groups are attributable to the reduced duration of viral shedding in rimantadine-treated subjects.