Immunogenicity of aerosol measles vaccine given as the primary measles immunization to nine-month-old Mexican children

Aerosol measles vaccination has been found to be more immunogenic than subcutaneous administration as a booster in school aged children, and immunogenic in 12-month-old children as a primary dose. The objective of the study was to evaluate immunogenicity to aerosol measles vaccine in 9-month-old children.MethodsNine-months-old infants received Edmonston-Zagreb measles vaccine by aerosol (103.58 CCID50/0.1 mL, estimated retained dose 102.81 CCID50) or subcutaneous route (104.28 CCID50/0.5 mL); cellular and humoral immunity and adverse events were assessed.ResultsMeasles-specific T cell proliferative responses developed in 42% of children given aerosolized vaccine compared with 67% of those who received subcutaneous vaccine (p = 0.01); the mean stimulation index (SI) was 4.4 ± 0.7 versus 6.9 ± 1, respectively, (p = 0.05). Seroconversion rates were 33 and 92% after aerosol or subcutaneous immunization (p < 0.001). Among infants who developed serologic responses, measles geometric mean titers (GMT; 95% CI) by neutralizing antibody assay were 215 mIU/mL (115–400) in aerosol vaccine recipients and 411 mIU/mL (345–490) in those given subcutaneous vaccine (p = 0.06).ConclusionsThe proportion of 9-month-old infants who developed cellular and/or humoral immunity to measles was lower in the aerosol group but measles antibody and T cell responses were comparable among those who developed measles immunity. Differences in response rates are attributable to the lower aerosol dose. Improving aerosol delivery or increasing the dose may enhance immunogenicity of primary aerosol measles vaccination in this age group.