Objective: To explore the cross immunity response between two similar strains of influenza A3 virus vaccine from 2007 to 2008.
Methods: Healthy adults aged 18-60 years old without history of flu vaccination were inoculated Anflu ™( 52 cases) or VAXIGRIP ® (137 cases) influenza split vaccine. A micro-hemagglutination inhibition (HI) assay was used to test the serum specimens collected from the subjects before and after vaccination. The seroconversion rate, geometric mean titer (GMT) and antibody protective rate were used to evaluate the effect.
Results: The seroconversion rates of Anflu ™ and VAXIGRIP ® tested by A/Hiroshima/52/2005 virus antigen were 82.7% (95%CI: 69.2% - 91.8%) and 80.3% (95%CI: 72.4% - 86.5%) respectively and there was no significant difference (χ(2) = 0.141, P > 0.05). The seroconversion rates of Anflu™ and VAXIGRIP ® tested by A/Wisconsin/67/2005 (H3N2)-like virus antigen were 71.2% (95%CI: 56.7% - 82.8%) and 73.7% (95%CI: 65.4% - 80.8%) respectively and there was no significant difference observed (χ(2) = 0.126, P > 0.05). GMT of Anflu™ and VAXIGRIP ® tested by A/Hiroshima/52/2005 virus antigen after vaccination increased 11.5 (95%CI: 7.5 - 17.5) times and 13.0 (95%CI: 10.0 - 16.9) times without significant difference (F = 0.497, P > 0.05). GMT of Anflu ™ and VAXIGRIP ® tested by A/Wisconsin/67/2005 (H3N2)-like virus antigen after vaccination increased 9.5 (95%CI: 6.3 - 14.3) and 10.9 (95%CI: 8.5 - 13.7) times, and there was no significant difference either (F = 0.554, P > 0.05). The antibody protective rate of two vaccines before and after immunity tested by A/Hiroshima/52/2005 virus antigen were 48.1% and 54.7% before vaccination and 98.1% and 95.6%after vaccination respectively without significant difference (χ(2) = 0.135 - 0.673, P > 0.05). The antibody protective rates of two vaccines tested by A/Wisconsin/67/2005 (H3N2)-like virus antigen were 11.5% and 13.9%before vaccination and 80.8% and 86.1%after vaccination respectively, and there was no significant difference (χ(2) = 0.178 - 0.834, P > 0.05). But the results tested by A/Hiroshima/52/2005 virus antigen were higher than those of A/Wisconsin/67/2005 (H3N2)-like virus antigen (χ(2) = 7.111 - 52.155, P < 0.01).
Conclusion: The two similar seasonal influenza vaccine strains recommended by WHO had a good cross immunity response, but the systematic error of test existed in two similar stains and the same strains should be used.