Antibody responses against antigens in the 2011-2012 influenza vaccine at 21 days post vaccination were analyzed in 264 individuals aged 50-80 years. At Days 0 and 21, sera were tested for hemagglutination-inhibition titers against these vaccine strains and at Day 0 against a panel of 15 historical seasonal strains.:
Concerns about influenza vaccine effectiveness in older adults and the role of influenza strains encountered earlier in life led to this study.
The proportions of participants with seroprotective titers ≥1:40 to the vaccine strains at Days 0 and 21, respectively, were 37% and 66% for A(H1N1) and 28% and 63% for A(H3N2). An increasing number of responses ≥1:40 against historical strains was associated with seroprotective responses after vaccination among participants with a titer<1:40 at Day 0 for A(H1N1) and A(H3N2) vaccine strains (P<0.01). In multivariable regression analyses among those with Day 0 titer<1:40, after controlling for age, sex, race, site and diabetes, Day 21 titers ≥ 1:40 for the vaccine A strains were significantly more likely as the number of seroprotective responses against historical strains increased (A(H1N1) odds ratio [OR] = 1.41, 95% confidence interval [CI] = 1.09-1.82 and A(H3N2) OR = 1.32, 95% CI = 1.07-1.62). The likelihood of seroconversion was significantly higher with an increasing number of responses to historical strains for A(H3N2) only (OR = 1.24, 95% CI = 1.01-1.52). Seroconversion was significantly less likely as Day 0 vaccine strain titers increased.
Seroprotective titers after influenza vaccination increased as the number of responses to historical strains increased.
Ross TM, Lin CJ, Nowalk MP, Huang HH, Spencer SM, Shay DK, Sambhara S, Sundaram ME, Friedrich T, Sauereisen S, Bloom CE, Zimmerman RK. (2014). Influence of pre-existing hemagglutination inhibition titers against historical influenza strains on antibody response to inactivated trivalent influenza vaccine in adults 50-80 years of age. Human vaccines & immunotherapeutics, 10(5)