Figure 1

Serum HAI antibody titers for seasonal influenza viruses after vaccination in mice. Immunologically naïve DBA/2J mice were vaccinated intramuscularly (i.m.) three times at four-week intervals with quadrivalent (left) or heptavalent (right) formulations of COBRA recombinant HA and NA proteins, with AddaVax™ as adjuvant. Sera collected two weeks after final vaccination were used for HAI assay against a panel of (a, b) H1N1 and (c, d) H3N2 viruses. The virus strains are listed along the x-axis. The y-axis indicates the log₂ HAI titers for each vaccinated group and presents them as absolute mean values ± SEM. The dotted lines indicate HAI titers ranging from 1:40 (lower line) and 1:80 (upper line). Statistical differences between quadrivalent and heptavalent vaccine groups were analyzed using multiple unpaired t-tests by GraphPad Prism 9 software (GraphPad, San Diego, CA, USA). A p value of less than 0.05 was defined as statistically significant (*, p < 0.05; **, p < 0.01; ***, p < 0.001; ****, p < 0.0001).