Evaluation of immunogenicity of trivalent split-vinus influenza vaccine among elderly populations
LI Pingping1, LUO Li1, WU Yifeng1, YE Lixia2
1. Department of Immunization, Jiangbei Center for Disease Control and Prevention, Ningbo, Zhejiang 315020, China; 2. Ningbo Center for Disease Control and Prevention, Ningbo, Zhejiang 315000, China
Abstract：Objective To investigate immune responses to influenza virus infections and the immunogenicity of trivalent split-virus influenza vaccine among elderly populations in Jiangbei District, Ningbo City, so as to provide the support for promoting influenza vaccination among elderly populations. Methods The elderly populations at ages of 60 years and older were recruited in Jiangbei District of Ningbo City from September to November, 2020, and the participants were assigned to the vaccination group and the control group according to vaccination intention. The titers of haemagglutination inhibition ( HI ) antibodies against influenza viruses A ( H1N1 and H3N2 ) and BV were measured using the micro HI test prior to vaccination and 30 days post-vaccination, and the protective rate, geometric mean titer ( GMT ) and seroconversion rate of antibodies were analyzed before and after vaccination. Results There were 290 participants in the vaccination group, including 132 men (45.52% ), and 290 controls, including 132 men ( 45.52% ). There were no significant differences between the vaccination group and the control group in terms of the protective rate or GMT of antibodies against influenza viruses A ( H1N1 and H3N2 ) and BV prior to vaccination ( P>0.05 ). Following vaccination, the protective rates of antibodies against influenza viruses A ( H1N1 and H3N2 ) and BV were 98.62%, 94.14% and 88.28%, and the GMT of antibodies against influenza viruses A ( H1N1 and H3N2 ) and BV increased by 9.26, 6.19 and 10.09 folds, while the seroconversion rates of antibodies against influenza viruses A ( H1N1 and H3N2 ) and BV were 78.62%, 68.28% and 71.38%, respectively. The protective rates, GMT and seroconversion rates of antibodies against influenza viruses A ( H1N1 and H3N2 ) and BV were all significantly greater in the vaccination group than in the control group post-vaccination ( P<0.05 ). A lower increase was seen in the GMT of antibodies against the influenza virus BV among residents at ages of 80 years and older (increase by 7.91 folds) than among residents at ages of 70 to 79 years ( increase by 12.53 folds ) and 60 to 69 years (increase by 13.32 folds) in the vaccination group post-vaccination ( P<0.05 ), and the seroconversion rate of antibodies against the influenza virus BV was significantly lower in residents at ages of 80 years and older ( 62.57% ) than in those at ages of 70 to 79 years ( 83.33% ) ( P<0.05 ), while the positive conversion rate of antibodies against the influenza virus A ( H3N2 ) was significantly lower in residents at ages of 80 years and older ( 62.57% ) than in those at ages of 60 to 69 years ( 91.30% ) ( P<0.05 ). Conclusions Low-level immune responses are detected to antibodies against influenza virus A ( H3N2 ) and BV among elderly populations in Jiangbei District of Ningbo City, and trivalent split-virus influenza vaccine shows a high immunogenicity among elder populations. An emphases on improvements in coverage of influenza vaccination among elderly populations at ages of 60 to 69 years, and development of influenza vaccines with a higher protective efficacy for residents at ages of 80 years and older are recommended.
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