Results of the single-radial-diffusion test with formaldehyde-treated influenza virus

We found reduced values for formaldehyde-treated influenza virus in the single-radial-diffusion test by comparison with non-treated virus. The reduction correlates with the formaldehyde concentration. Hemagglutination and neuraminidase activities were not affected by the same treatment. We therefore suggest that this reduction is not based on antigen destruction.