A single dose of an ISCOM influenza vaccine induces long-lasting protective immunity against homologous challenge infection but fails to protect Cynomolgus macaques against distant drift variants of influenza A (H3N2) viruses.

Since the production of influenza vaccines is complicated by the continuous variation of these viruses, it would be desirable to develop vaccines that induce cross-protective immunity against influenza virus strains that circulate in subsequent winter epidemics. We have recently demonstrated that antibodies induced after vaccination with an immune stimulating complex (ISCOM)-based vaccine exhibited a certain degree of cross-reactivity with other influenza virus strains. In the present study, ISCOM-based vaccines were evaluated retrospectively by testing the protective immunity induced by ISCOM prepared with the membrane glycoproteins of A/Philippines/2/82 against the more recent strain A/Netherlands/18/94 in monkeys with or without a history of prior infection with an A/Philippines/2/82-like virus. It was found that the monkeys immunized with the A/Philippines/2/82 ISCOM were not protected from challenge infection with A/Netherlands/18/94. On the other hand, vaccination of monkeys which experienced a prior infection with an influenza A/Philippines/2/82-like virus, with a single dose of ISCOM vaccine induced long-lasting protective immunity against challenge infection with the homologous virus A/Netherlands/18/94.