CROSS-PROTECTION OF MICE IMMUNIZED WITH DIFFERENT INFLUENZA-A (H2) STRAINS AND CHALLENGED WITH VIRUSES OF THE SAME HA SUBTYPE

Cross-protection of mice immunized with inactivated preparations of hu man and avian influenza A (H2) viruses was determined after lethal inf ection with mouse-adapted (MA) variants of human A/Jap x Bell/57 (H2N1 ) and avian A/NJers/78 (H2N3) viruses. The MA variants differed from t he original strains by acquired virulence for mice and changes in the HA antigenicity. These studies indicated that mice vaccinated with hum an influenza A (H2) viruses were satisfactorily protected against chal lenge with A/Jap x Bell/57-MA variant; the survival rate was in the ra nge of 61%-88.9%. Immunization of mice with the same viral preparation s provided lower levels of protection against challenge withA/NJers/78 -MA variant. Vaccination of mice with the avian influenza A (H2) virus es induced better protection than with human strains against challenge with both MA variants. Challenge with A/NJers/78-MA variant revealed that 76.2%-95.2% of animals were protected when vaccinated with avian influenza virus strains isolated before 1980, and that the protection reached only 52.4%-60.0% in animals vaccinated with strains isolated i n 1980-1985. The present study revealed that cross-protection experime nts in a mouse model could provide necessary information for the devel opment of appropriate influenza A (H2) virus vaccines with a potential for these viruses to reappear in a human population.