Immune responses to mumps vaccine in adults who were vaccinated in childhood

Background. In a mumps outbreak in the United States, many infected individuals were adults who had received 2 doses of mumps vaccine. The persistence of cellular immunity to mumps vaccine has not been defined. Methods. This was an observational, nonrandomized cohort study evaluating cell-mediated and humoral immunity to mumps in 10 vaccinated and 10 naturally immune adults. Mumps-specific T cell activation and interferon (IFN)-gamma production were measured using lymphoproliferative and flow cytometry assays, and mumps immunoglobulin (Ig) G was measured using enzyme-linked immunosorbent assay. Results. T cell immunity to mumps was high in both groups; 70% of vaccinated and 80% of naturally immune individuals had a positive (>= 3) stimulation index (SI) (P = 1.0). The mean percentages of mumps-specific CD4(+) T cells that expressed CD69 and produced IFN-gamma were equivalent in the 2 groups: 0.06% and 0.12%, respectively (P = .11). The mean SIs in the groups were also equivalent, although IFN-gamma concentrations from cultures stimulated with mumps antigen were higher in naturally immune adults than in vaccinated adults (P <= .01). All adults were positive for mumps IgG. Conclusion. T and B cell immunity to mumps was detected in adults at least 10 years after immunization. Except for IFN-gamma release, responses in vaccinated adults paralleled those observed in naturally immune individuals.