Relative antigenicity in mice of H1N1, H3N2 and B strains present in inactivated influenza virus vaccines.

The results of a study on serum HAI and neutralizing antibodies induced in mice by whole influenza virus vaccines containing A/Brazil/11/78 (H1N1), A/Bangkok/1/79 (H3N2) and B/Singapore/222/79 viruses are reported. According to the GMT of HAI, the antigenic potency of the three vaccine strains appear to be different. The A/Brazil/11/78 antigen induced the lowest HAI antibody responses and the A/Bangkok/1/79 antigen the greatest. This behaviour, with a few exceptions, was noted regardless of the HA amount (0.08 microgram 0.4 microgram, 2 micrograms) of each strain present in the vaccine, the number of doses (one or two), or the kind of preparation (monovalent or trivalent). The data obtained with the neutralization test with vaccines with medium HA content are concordant with previous findings. On the basis of the ratios of the GMT of the neutralizing antibodies to the GMT of the HAI antibodies, it was concluded that the HAI antibodies to A/Bangkok/1/79 antigen possess, on the whole, a neutralizing activity that is higher than that found for the HAI antibodies to A/Brazil/11/78 and B/Singapore/222/79 strains. For the latter strains, the neutralizing activity increased after the second dose. The observation of the different degrees of antigenicity of the three vaccine strains suggests that, with currently used inactivated influenza virus vaccines containing equivalent amounts of all three antigens, the dosage should be taken into consideration when the vaccines are used for subjects lacking in previous exposure to vaccine strains.