Influenza in the United Kingdom 1977-1981.

The laboratory surveillance of influenza in the UK has continued to demonstrate the regularity of influenza outbreaks each winter even in the absence of increase in the other indices which reflect the morbidity and mortality associated with influenza. The period of five years from 1976 to 1981 has seen the appearance of a second sub-type of influenza. A with the return of the historic H1N1 virus; and the continued circulation of H3N2 concurrently with H1N1 virus. Variants of both these influenza A viruses have been demonstrated as well as further changes in the strains of influenza B virus isolated during this time.