Background: High attack rates among vaccinated young adults reported during the 2006 mumps outbreak in the United States heightened concerns regarding mumps vaccine failure.
Methods: Serum specimens from university students and staff were tested for mumps immunoglobulin (Ig) G by enzyme immunoassay (EIA). A subset of participants vaccinated for < or =5 years and > or =15 years were tested by neutralizing antibody (NA) assay. Persons seronegative by EIA were offered a third dose of measles-mumps-rubella vaccine (MMR3), and serum specimens were obtained 7-10 days and 2-3 months after its administration.
Results: Overall, 94% (95% confidence interval [CI], 91%-96%) of the 440 participants were seropositive. No differences existed in seropositivity rates by sex, age, age at receipt of the second dose of MMR vaccine (MMR2), or time since receipt of MMR2 (P = .568). The geometric mean titer (GMT) of NA among persons vaccinated with MMR2 during the previous 1-5 years was 97 (95% CI, 64-148), whereas, among those vaccinated > or =15 years before blood collection, the GMT was 58 (95% CI, 44-76) (P = .065). After MMR3, 82% (14/17) and 91% (10/11) seroconverted in 7-10 days and 2-3 months, respectively.
Conclusions: Lower levels of NA observed among persons who received MMR2 > or =15 years ago demonstrates antibody decay over time. MMR3 vaccination of most seronegative persons marked the capacity to mount an anamnestic response.