| laboratory-based surveillance of influenza virus in the united states during the winter of 1977-1978. i. periods of prevalence of h1n1 and h3n2 influenza a strains, their relative rates of isolation in different age groups, and detection of antigenic variants. | influenza a (h3n2) viruses were isolated from outbreaks and epidemics of disease during the period december 1977 to march 1978. for the last two months of this period, h1n1 strains of influenza a were also responsible for epidemics. in some regions (e.g., hawaii) co-circulation of h1n1 and h3n2 strains occurred, whereas in other regions (e.g., wisconsin) isolation of h3n2 strains had almost ceased prior to isolation of h1n1 strains. few influenza b isolates were reported. analysis of the ages of ... | 1979 | 507036 |