Influenza viruses, 1957-60.

During the period 1957-60 large numbers of influenza A viruses were received at the World Influenza Centre from countries throughout the world. With one exception all the strains were antigenically closely related to the A2 viruses isolated early in the Asian influenza epidemic, and strikingly different from the A1 strains of the previous decade. The A2 viruses were very uniform antigenically and in other in vitro characteristics such as insensitivity to the beta-inhibitor of agglutination. However, many of the strains, particularly during the early stages of the epidemic, showed a low avidity for antibody.At the same time as the influenza A viruses showed a large antigenic change the influenza B viruses showed a lesser antigenic change from earlier influenza B viruses. As with influenza A, the new influenza B viruses have replaced earlier B strains.In 1960 one strain of influenza virus A1 was recovered from a soldier in England. Evidence is presented that this could not be explained as a laboratory pick-up and the suggestion is put forward that this patient may have harboured virus in latent form for many years.