Abstract
An immunodiffusion technique in agarose is described for assay of complement-fixing antibodies against the type-specific soluble antigen of influenza virus. Under the test conditions, positive human serum produced a definite unlysed zone around the well, and the annulus area showed a high correlation with the antibody level in a conventional complement fixation test with log2 serum titer. This paper also describes the use of this method as a diagnostic procedure for the assay of antibodies against soluble antigens of influenza A and B viruses in paired human sera collected from persons infected with the virus or who received ether-split vaccine. This method appears to more sensitive and gives more consistent results for serodiagnosis of infection cases than do the hemagglutination inhibition, neuraminidase inhibition, and complement fixation tests. Our results suggest that the single radial complement fixation test can provide a simple and reliable method for serodiagnosis of influenza virus infection.