Stato dell'immunità della popolazione milanese verso il nuovo ceppo di tipo B, B/Hong Kong/8/73 e studio del potere immunizzante del vaccino di vecchia composizione. Immunity status of the Milanese population towards B-Hong Kong-8-73, the new B type strain and study of the immunizing activity of the old composition vaccine

In view of the possibility that the new B Hong Kong strains which have a completely new hemoagglutinin would spread during the epidemic season, a serological survey was carried out on 180 serum samples collected between November and December 1972 in Milan from people aged 4 to over 60 yr. Because of limited data indicating that the neuraminidase of the new strains is antigenically related to that of earlier B strains, both hemagglutination inhibiting antibodies (HIA) and antineuraminidase antibodies (ANab) against the B/Hong Kong/8/773 strain were titrated. To gain information on the possibility that, lacking adequate aliquots of the new vaccine, some degree of protection could be conferred also by current vaccine preparations, both types of antibody were titrated in sera of children given a polyvalent vaccine including the strain B/Roma/67. The results indicated that HIA are almost absent in the Italian population since it was found only at low titers (1:10 - 1:20) in 12% of the sera, while ANab were present in 28 out of 57 sera examined and their level was over 1:20 in 25%. Judging from the behavior of the HIA, the response to the vaccine including the B Roma/67 strain was very poor. None of the 32 children developed antibody at titer >1:20. On the contrary ANab were found in 22 of the children (out of 25 examined) after a single dose of vaccine and all but one had ANab at titer >1:20 after the second dose. It is concluded that a certain degree of protection against the new B viruses could be afforded also by current vaccines.