Evaluation of age-related differences in the immunogenicity of a G9 H9N2 influenza vaccine

Abstract

Avian influenza A/H9N2 viruses can infect people and are viruses considered to be a potential pandemic threat. Prior studies with an inactivated G1 clade H9N2 vaccine reported that persons born before 1968 were more likely to have an immune response than younger subjects. We performed a randomized, double-blind trial to evaluate whether immune responses following immunization with an inactivated, unadjuvanted influenza G9 H9N2 vaccine prepared from A/chicken/Hong Kong/G9/97 virus were more frequent in persons born in 1964 or earlier (44-59 years) than in those born in 1970 or later (18-38 years). One hundred twenty one persons were randomized to receive two doses of either 7.5- or 30-mcg of hemagglutinin intramuscularly. Post-vaccination serum antibody responses as measured by hemagglutination inhibition and microneutralization were either similar in the two age cohorts or greater in the younger age group. Persons born before 1968 were not more likely to respond to a G9 H9N2 influenza vaccine than persons born in 1970 or later.

Figure 1

Reverse cumulative distributions by age group and clade for HAI (A) and MNt (B) serologies measured at day 0. Data are shown for each age group (18–38 years and 44–59 years) and H9N2 clade (G9 and G1).

Figure 2

Reverse cumulative distributions for the G9 strain by dosage and age group as measured by HAI (A and B) and MNt (C and D) for the day 28 (A and C) and day 56 (B and D) time points. Data are shown for each age group (18–38 years and 44–59 years) and dosage group (7.5 and 30 mcg).

Figure 2

Reverse cumulative distributions for the G9 strain by dosage and age group as measured by HAI (A and B) and MNt (C and D) for the day 28 (A and C) and day 56 (B and D) time points. Data are shown for each age group (18–38 years and 44–59 years) and dosage group (7.5 and 30 mcg).