BOOSTING EFFECT OF A 2ND DOSE OF MEASLES-VACCINE GIVEN TO 12-YEAR-OLDCHILDREN

In Sweden, a two-dose programme of vaccination against measles, mumps and rubella (MMR) was introduced in 1982 and the target groups were ch ildren aged 18 months and 12 years. In 1993 the first age group of 12- year-olds that were vaccinated with MMR at 18 months will appear. The majority of the 12-year-old vaccinees for many years, however, had alr eady been vaccinated against measles and the MMR measles component was thus a booster dose. As the benefit of a booster dose against measles has been questioned, this was studied in a group of 163 12-year-old c hildren, 122 of whom had been vaccinated against measles as young chil dren. Of the 41 unvaccinated children, 23 had a history of clinical me asles. The mean neutralizing titre level of the earlier vaccinated chi ldren, prior to the booster, was lower than that of the naturally immu ne children (reciprocal titre level 8 versus 20). After the booster th e corresponding titre levels were 13 and 23. Among the seronegative ch ildren receiving their first dose, this figure amounted to 14. A moder ate rise in titre was seen in those with low prevaccination titres. As the antibody protection afforded by vaccination was slightly lower th an that of natural infection, even after a booster, follow-up studies must be recommended to evaluate the long-term protection of both a sin gle and a two-dose programme.