Background: Since 1990, most US schoolchildren have received a second dose of measles-mumps-rubella vaccine (MMR2) at kindergarten entry. The objective of the present study was to evaluate the short- and long-term mumps immunogenicity of MMR2.
Methods: At enrollment in 1994-1995, children (n=308) in a rural Wisconsin health maintenance organization received MMR2 at age 4-6 years. A comparison group of older children (n=308) was vaccinated at age 9-11 years. Serum samples were collected over 12 years. Mumps antibody levels were evaluated by plaque-reduction neutralization (lowest detectable titer, 10).
Results: Before MMR2, the geometric mean titer (GMT) for the younger group was 33; no subject was seronegative, but 16% had the lowest detectable titer. In response to MMR2, the GMT tripled to 97, and the proportion with low titers diminished to 3%. Four-fold boosts occurred among 54%, but only 3% were positive for immunoglobulin M. Twelve years after MMR2, the GMT declined to 46, the proportion with titers<or=10 was not significantly different from the pre-MMR2 proportion, and 5% were seronegative. The older group showed similar patterns, and at age 17 years both groups had comparable antibody levels.
Conclusions: The mumps antibody response to MMR2 was vigorous, but over a 12-year period titers declined to levels similar to pre-MMR2 titers. No advantage was apparent in delaying MMR2 from kindergarten to middle school.