Immunity to rubella before and after vaccination against measles, mumps and rubella (MMR) at 12 years of age of the first generation offered MMR vaccination in Sweden at 18 months

Abstract

In 1982, a two-dose programme of vaccination against measles, mumps and rubella (MMR) at the ages of 18 months and 12 years was introduced in Sweden. In 1992–1993, the first group of children vaccinated at 18 months reached the age of 12, i.e. the time for a second dose. In connection with this 12-year vaccination, 376 children were recruited, investigated concerning earlier MMR vaccination and bled prior to and 2 months after the immunization. Two hundred and twenty of them had a documented, earlier MMR vaccination and 156 had not. The latter were classified as unvaccinated. The antibody status against rubella was measured by the haemolysis-in-gel method. Prior to the present vaccination, 3% of the earlier vaccinated group totally lacked any sign of antibodies. In the presumably unvaccinated group, this figure was 76%. After the vaccination all children showed signs of antibody acitivity and all reached the antibody level of ≥15 international units, i.e. in our tests a zone dia. of approx 8 mm. However, the secondly vaccinated children ended up with a mean antibody level of 10.7 mm which was slightly lower than the level, i.e. 11.0 mm of those lacking earlier vaccination history and prevaccination seronegative. The earlier unvaccinated but pre-immune children reached a mean level of 11.2 mm. In general, those with relatively high, pre-vaccination, antibody levels reacted less to the booster than those with low or no pre-vaccination immunity. The booster thus appeared to restore the antibody levels of the low-titre children.