Influenza vaccine in unprimed children: improved immunogenicity with few reactions following one high dose of split-product vaccine.

Thirty-one unprimed children and young adults received an influenza A/USSR/77 vaccine containing 43 microgram of hemagglutinin. Their HAI antibody response was compared to that in 92 age-matched individuals from the 1978 national influenza immunization trial who received 10 and 4 microgram HA vaccines. A dose-related antibody response was observed after the first vaccine doses in the 7- to 12- and 13- to 25-year-old groups. An HAI titer greater than or equal to 40 was present in 81% and 93% of 43 microgram HA recipients, in 38% and 43% of 10 microgram HA recipients, and in 24% and 12% of 4 micrograms HA recipients respectively. The antibody response to the 43 microgram HA dose was significantly higher than was the response to the 10 and 4 microgram HA doses. The local and systemic side effects were not significantly different among the three vaccine groups and the placebo group. Thus, a high dose of influenza A/USSR/77 split-product vaccine given to unprimed children and young adults stimulated presumably protective levels of antibody and was free of a significant incidence of side effects.

Persistence of maternal antibody in infants beyond 12 months: mechanism of measles vaccine failure.

A serologic study was made in 34 children immunized against measles at the age of 12 months. Using a sensitive virus neutralization test, it was found that many of the children had pre-existing maternal antibody to measles virus. Children with high pre-existing antibody titers failed to seroconvert. Children with lower pre-existing antibody titers seroconverted, but the resulting antibody titer was significantly lower than in children without pre-existing antibody titer. The results of this study demonstrate a probably mechanism for measles vaccine failure in 12-month-old children and support the recommendation of the Public Health Service Advisory Committee on Immunization Practices to postpone measles vaccination to 15 months of age.