PERSISTENCE OF ANTI-MUMPS VIRUS-ANTIBODIES AFTER A 2 DOSE MMR VACCINATION - A 9-YEAR FOLLOW-UP

A two-dose vaccination program against measles, mumps, and rubella (MMR) viruses was started in Finland in 1982. In this program the trivalent MMR-II vaccine (MSD, USA) was offered to children at the ages of 14-18 months and 6 years followed by revaccination 4-5 years later. The vaccination coverage has been high (97%) and MMR infections have practically been eliminated in the Finnish population. In a serological follow-up program sequential serum samples were obtained from 254 children (127 14-18-month-old vaccinees and 127 6-year-old vaccinees) curing a 9-year follow-up period Anti-mumps virus antibody titers were determined by enzyme immunoassay using purified whole mumps viruses as the antigen. In seronegative (n=120) 14-18-month-old vaccinees the seroconversion rare was 86% (geometric mean titer 1/1670 +/- 1/270). The antibody levels fell vapidly (significance p<0.01) within the first year of follow-up (mean titer 1/1080 +/- 1/190), but remained relatively stable in subsequent years. After revaccination the seropositivity rate was 95% (mean titer 1/2310 +/- 1/260) and declined move slowly thereafter to 86% (mean titer 1/1510 +/- 1/210) at year 9 of follow-up. The mean antibody titer was significantly (p<0.05) higher 4 years after the second MMR vaccination when compared with the corresponding time point after the first vaccination. In 6-year-old seronegative vaccinees the increase and decay of anti-mumps vine antibodies after the first MMR vaccination was similar to that seen in the group of younger vaccinees. A two-dose MMR vaccination protocol resulted in a high mumps immunity level in the vaccinated population.