The Serological Comparison of Strains of Influenza Virus

Abstract

SUMMARY: The antigens of eight strains of influenza virus were compared by a simple and economical complement-fixation technique in which drops on Perspex sheets replaced larger volumes of reagents in racks of tubes. By this means more extensive tests were made with a limited supply of material than by standard tube techniques. The specific antisera were prepared in mice, thus avoiding the elaborate isolation precautions necessary for ferrets, and sera from large groups were pooled to minimize individual variations between animals. The antigens were standardized in terms of the amount of complement fixed in the presence of excess homologous antiserum. The comparison of the strains is presented in the form of index numbers, ranging from 0 to 1·0: 1·0 represents complete identity of two strains, while the smaller numbers are taken to represent the degree of antigenic relationship between strains. Of the six strains examined which were isolated in different years, all were serologically distinct though the two B strains were closely similar and two of the A strains were fairly closely related. On the other hand, the three strains of influenza A virus isolated in 1947, two in London and one in the U.S.A., were identical.