Surveillance of the antibody status to current influenza strains in the Norwegian population. 1: Method of serum sampling and evaluation of the A/USSR/77 (H1N1) impact in various age groups in 1978.

Every autumn approximately 900 randomly selected sera from various regional bacteriological laboratories are received at the NIPH and assayed for the presence of haemagglutination-inhibition antibodies to current influenza strains. After three years of preliminary investigations the system is now working successfully. It is possible, in retrospect, to assess the impact of various influenza strains in different age groups and regions of the country. In particular, after the reappearance of the H1N1 subtype (the "Russian influenza") in Europe in January 1978, the sera collected in Norway during a 3-week period in October 1978 clearly showed that those under the age of 25 years, and especially teenagers between 13 and 16 years of age, were struck by this virus. This was unexpected since there was hardly any influenza morbidity associated with this "new" strain recorded in the winter of 1978.