Vaccination as a strategy to reduce the emergence of amantadine- and rimantadine-resistant strains of A/Chick/Pennsylvania/83 (H5N2) influenza virus.

The influenza A virus (A/Chick/Pennsylvania/83 (H5N2) that caused up to 80% mortality in chickens provided a model system for testing the efficacy of chemotherapeutic agents against highly virulent influenza virus. Amantadine and rimantadine administered to chickens in drinking water were efficacious both prophylactically and therapeutically. However, under conditions simulating natural transmission of virus amantadine and rimantadine-resistant viruses arose and were transmitted to contact birds, causing mortality. Simultaneous administration of inactivated H5N2 vaccine and amantadine provided protection. Thus, chemotherapy may be useful in the treatment of a highly pathogenic influenza virus outbreak in humans or other animals when used in combination with vaccine.