Epidemiology of influenza in Lower Saxony during the period 1968-1978 with particular emphasis on subtypes A(H3N2) and A(H1N1) in winter 1977-78.

The influenza surveillance in Lower Saxony is based mainly on laboratory investigations, and especially those which involve the isolation of influenza viruses throughout the year. These investigations have provided information on the circulation of influenza viruses and of the antigenic drift during the Hong Kong period which resulted in many different variants. Since the advent of the Hong Kong virus subtype, a high excess mortality was observed only in the winter of 1969-70. In most of the other years there was a low excess mortality which coincided with the circulation of the influenza A viruses in the population. During the last winter 1978, influenza A viruses were not isolated before February. In February and March, the two distinct subtypes H3N2 and H1N1 circulated simultaneously. The influenza A(H1N1) virus attacked only children and young adults whereas the patients infected with influenza A(H3N2) virus ranged over all age groups.