National influenza experience in the USA, 1968-69.

An extensive outbreak of Hong Kong influenza occurred in the USA during the autumn and early winter of 1968-69. Introduction and seeding of the virus occurred in September and early October as individuals returned from the Far East. Civilian outbreaks did not develop until late October and November. By 28 December, all States had experienced influenza outbreaks. Limited information concerning age- and sex-specific attack rates indicates that all age segments of the population were equally involved. Significant excess pneumonia-influenza mortality occurred in all 9 geographical areas of the country and followed influenza activity by several weeks. Influenza B activity was documented in 37 States during the winter.