In the last decade, several
mumps outbreaks were reported in various countries despite high vaccination coverage. In most cases, young adults were affected who have acquired immunity against
mumps solely by vaccination and not by previous wild-type mumps virus
infection. To investigate
mumps-specific antibody levels, functionality and dynamics during a
mumps epidemic, blood samples were obtained longitudinally from 23 clinical
mumps cases, with or without a prior history of vaccination, and from 20 healthy persons with no serological evidence of recent mumps virus
infection. Blood samples from
mumps cases were taken 1-2 months and 7-10 months after onset of disease. Both vaccinated and unvaccinated
mumps cases had significantly higher geomean concentrations of
mumps-specific
IgG (resp. 13,617 RU/ml (95% CI of 9,574-19,367 RU/ml) vs. 1,552 (445-5412) RU/ml at 1-2 months; and 6,514 (5,247-8,088) RU/ml vs. 1,143 (480-2,725) RU/ml at 7-10 months) than healthy controls (169 (135-210) RU/ml) (p = 0.001). Patterns in virus-neutralizing (VN) antibody responses against the
mumps vaccine virus were similar, vaccinated and unvaccinated
mumps cases had significantly higher ND50 values at both time points of sampling (resp 4,695 (3,779-5,832) RU/ml vs. 1,533 (832-2,825) RU/ml at 1-2 months; 2,478 (1,968-3,122) RU/ml vs. 1,221 (1,029-1,449) RU/ml at 7-10 months) compared with (previously vaccinated) healthy controls (122 (196-76)) RU/ml) (p = 0.001) The unvaccinated
mumps cases had significantly lower
mumps-specific
IgG and VN antibody concentrations at both sampling points compared with previously vaccinated cases, but their antibody concentrations did not differ significantly at the 2 time points. In contrast, the
mumps-specific
IgG and VN antibody concentrations of the previously vaccinated
mumps cases were significantly higher within the first 2 months after onset of
mumps and declined thereafter, characteristic for a secondary response. A moderate correlation was found between the level of
mumps-specific
IgG serum
antibodies and VN
antibodies for the
mumps cases (r = 0.64; p<0.001).