Formulation of inactivated influenza vaccines for providing effective cross-protection by intranasal vaccination in mice.

Attempts were made to formulate an inactivated influenza vaccine to provide effective cross-protection by intranasal vaccination in mice. Mice were immunized with a nasal site-restricted volume of various HA vaccines (split-product virus vaccines), prepared from some of the H1N1 subtype viruses which circulated in humans from 1934 to 1986, together with cholera toxin B subunit (CTB) as an adjuvant. Four weeks later, they were challenged intranasally with a lethal dose of the earliest H1N1 virus strain, A/PR/8/34 (PR8) or the latest virus strain, A/Yamagata/120/86 (Yamagata/86). The adjuvant-combined vaccines, prepared from drift H1N1 viruses, A/Kumamoto/37/79 and A/Bangkok/10/83, provided a higher degree of cross-protection against a challenge with Yamagata/86 than with PR8. A booster with another drift virus vaccine given 4 weeks after the primary vaccination increased the protection against Yamagata/86; the effect was higher when mice were vaccinated with a later strain as the second antigen than when boosted with PR8. These results suggest that vaccination with a later virus strain followed by another later strain in a two-dose nasal vaccination regimen gives effective cross-protection against the current epidemic virus strains.