A seroconversion study of the measles component of the MMR vaccine in adolescents of the town of Sabrosa.

Abstract

The Portuguese national programme of vaccination has instituted a two-dose MMR vaccine schedule. The second dose of MMR (measles-mumps-rubella combined vaccine) is given at 11-13 years of age, for both sexes. This study was conducted to evaluate the duration of immunity of the monovalent measles vaccine, and the efficacy of a second dose given as MMR. MMR (Triviraten Berna with the strain Edmonston-Zagreb) was given to the 38 participants. Blood samples were collected before and after vaccination. Thirty-six participants had been vaccinated with measles monovalent vaccine during childhood. To measure anti-measles IgG (mIgG), an enzyme immunoassay was used. Participants were classified as "susceptible" or "immune", using 200 mIU/ml (milli international units per millilitre) as the threshold for "immune". Geometric mean concentration (GMC) of mIgG was 1401 mIU/ml in prevaccination sera (n = 38). Thirty-five (92%) of the adolescents were "immune". Only the two unvaccinated had a positive measles history. GMC in the sera of the 36 vaccinated participants was 1301 mIU/ml. Neither the time since measles vaccination nor age at vaccination were correlated with the levels of mIgG. After receiving MMR, all adolescents became "immune". GMC of mIgG was 2879 mIU/ml in postvaccination sera (n = 38). In 28 (74%) participants, mIgG levels increased after receiving MMR. Mean concentration increase was 1082 mIU/ml. For measles, results support the use of a two-dose MMR vaccine schedule in Portugal.