Immunogenicity and reactogenicity to Haemophilus influenzae type b (Hib) conjugate vaccine among rural Alaska adults

Background: Despite routine vaccination and declining disease rates, Haemophilus influenzae type b (Hib) invasive disease still occurs in rural Alaska. Colonization studies indicate persistent transmission of Hib among village residents, including adults. As part of a project to eliminate Hib carriage in three rural villages, we evaluated a cohort of Alaska adults for antibody response and reactogenicity to a single dose of Hib conjugate vaccine (HbOC). Methods: Seventy-five previously unvaccinated, randomly-selected adults in one village received a single dose of HbOC vaccine and completed a side-effects diary. Sera and oropharyngeal specimens were collected at baseline, two months and one year. Results: No participants were colonized with Hib or reported serious side-effects. At baseline, 97% of adults had IgG anti-PRP concentrations >= 0.15 mu g/mL, 69% >= 1 mu g/mL, and 28% >= 5 mu g/mL. Two months post-vaccination, 100% of participants had concentrations >= 0.15 mu g/mL, 93% >= 1 mu g/mL, and 86% >= 5 mu g/mL. After 1 year, 98% had IgG anti-PRP concentrations >= 0.15 mu g/mL, 86% >= 1 mu g/mL, and 67% >= 5 mu g/mL. GMCs were 1.9, 33.3 and 8.4 mu g/mL at baseline, 2 months and 1 year post-vaccine, respectively (p < 0.01). Serum bactericidal activity increased from a baseline geometric mean titer of 2,205 to 8,349 two months post vaccination and declined to 1102 after one year. Conclusions: HbOC vaccine was immunogenic and well-tolerated among Alaskan adults. Nearly 90% of the adults developed an antibody level associated with protection against Hib colonization which persisted for 1 year in 67% of participants.