Background: Since 1989 the American Academy of Pediatrics and the ACIP have recommended a second dose of measles-mumps-rubella vaccine (M-M-R-II) at either school entry or age 11 to 13 years. Unfortunately few studies are available to compare responses to vaccine at the two ages. We performed a prospective trial to determine the persistence of antibody to measles, mumps and rubella vaccination in two age groups and the response to a second dose given at either 4 to 6 or 11 to 13 years.
Methods: Thirty-eight children 4 to 6 years old and 57 children 11 to 13 years old were given a second dose of M-M-R-II as they presented for yearly examinations. All had received the first dose at > or = 15 months of age. Measles and rubella antibody were measured by enzyme-linked immunosorbent assay (ELISA) and neutralizing antibody (NT) assay, and mumps antibody was measured by an ELISA method only. An IgM-ELISA antibody assay for measles was used in selected children. Prevaccination and 3- to 4-week post-vaccination sera were obtained. Measles ELISA, measles-neutralizing antibody (NT) and rubella-neutralizing antibody (NT) assays were performed in all children. Seventy-nine of the 95 children had sufficient sera for repeat measles tests, as well as mumps and rubella ELISA determinations.
Results: Before the second dose ELISA seropositivity rates for measles and mumps were not significantly different between the two groups. Rubella ELISA seropositivity was 67% in 11- to 13-year-olds, compared with 90% in 4- to 6-year-olds (P < 0.01), suggestive of waning immunity. Rubella NT seropositivity was also lower in 11- to 13-year-olds than in 4- to 6-year-olds (63% vs. 100%, P < 0.01). After revaccination, 100% of the children become seropositive for all 3 antibodies. We performed measles IgM-ELISA testing on all 17 measles-seronegative children, as well as 15 seropositive children and 19 children who were 1 month postvaccination with the first M-M-R-II at 15 months. The purpose was to determine whether the seronegative children were primary or secondary failures. Five of the 17 children with undetectable pre-second dose antibody made IgM measles antibody after revaccination, suggesting that they were primary vaccine failures.
Conclusions: Because all children became seropositive after revaccination, the age of administration can be based on the convenience of vaccine scheduling. However, in view of the apparent decline in rubella antibodies at 11 to 13 years, future studies of rubella vaccination should address the issue of whether earlier boosting leads to greater susceptibility at the time of reproductive age.