Antibody Response to Influenza A(H1N1)pdm09 Among Healthcare Personnel Receiving Trivalent Inactivated Vaccine: Effect of Prior Monovalent Inactivated Vaccine

Background. Few data are available on the immunogenicity of repeated annual doses of influenza A(H1N1) pdm09-containing vaccines. Methods.aEuro integral We enrolled healthcare personnel (HCP) in direct patient care during the autumn of 2010 at 2 centers with voluntary immunization. We verified the receipt of A(H1N1)pdm09-containing monovalent inactivated influenza vaccine (MIIV) and 2010-2011 trivalent inactivated vaccine (TIV). We performed hemagglutination inhibition antibody (HI) assays on preseason, post-TIV, and end-of-season serum samples. We compared the proportion of HCPs with HI titer a parts per thousand yen40 against A(H1N1)pdm09 per receipt of prior-season MIIV, current-season TIV, both, or neither. Results.aEuro integral At preseason (n = 1417), HI a parts per thousand yen 40 was significantly higher among those who received MIIV (34%) vs those who did not (14%) (adjusted relative risk [ARR], 3.26; 95% confidence interval [CI], 2.72-3.81). At post-TIV (n = 865), HI a parts per thousand yen 40 was lower among HCP who received MIIV and TIV (66%) than among those receiving only TIV (85%) (ARR, 0.93 [95% CI, .84-.997]). At end-of-season (n = 1254), HI a parts per thousand yen 40 was 40% among those who received both MIIV and TIV and 67% among those receiving only TIV (ARR, 0.76 [95% CI, .65-.88]), 52% among those who received MIIV only, and 12% among those receiving neither. Conclusions.aEuro integral HCP immunization programs should consider effects of host immune response and vaccine antigenic distance on immunogenicity of repeated annual doses of influenza vaccines.