CROSS-REACTION BUT NO AVIDITY CHANGE OF THE SERUM ANTIBODY-RESPONSE AFTER INFLUENZA VACCINATION

Pre- and post-vaccination sera form 19 volunteers were analysed by the haemagglutination inhibition (HI) test, virus neutralization (VN) ass ay and avidity enzyme-linked immunosorbent assay (ELISA). The sera wer e tested against the three strains in a commercial inactivated influen za vaccine; A/Beijing/353/89 (H3N2); A/Taiwan/1/86 (H1N1) and B/Yamaga ta/16/88. Additionally, a range of earlier strains and one newer isola te were assayed for HI- and VN-antibodies. Large variations in the pre -vaccination HI titres were observed for the viruses tested. However, 8-9 days after vaccination HI titres increased to above the assumed pr otective level (HI greater than or equal to 40) in most subject. Altho ugh a limited number of patients were analysed at each sampling point, the time-profile we observed in this study is consistent with data we have obtained in earlier trials (Cox, R.J. et al., Vaccine 1994, 12, 993-999). The VN titres, on the other hand, were low against all influ enza strains before and up to o 6 days, but increased rapidly 8-9 days after vaccination. A recent H3N2 isolate, A/Beijing/32/92 (H3N2), whi ch had drifted further away from the vaccine strain, reacted to low ti tres or were negative in both the HI and VN assays. No change in the s erum avidity to the influenza surface antigens was detected after vacc ination, whereas sera from subjects naturally infected with influenza showed an increase in avidity to the infecting virus strain. The incre ase and prolonged antigenic stimulus provided by the replicating virus .