This study was aimed to conduct a 3-year perspective study to observe the immunological effect of one-dose mumps-containing vaccine, monitor the incidence of mumps in vaccinated population aged 3-7 years，and provide basis for adjusting MMR immunization strategy in Jiangsu province, China.

in 3-7 years old children with high risk of mumps, epidemiological investigation of the serum IgG antibody level were conducted, and then a prospective observational cohort was established in the population with a history of mumps vaccination, and the incidence of mumps in each antibody level group will be observed, the relationship between different antibody levels and the incidence after mumps vaccinated were analyzed, to explore attenuation of mumps IgG antibody levels in the body,S79 vaccine strain against F genotype mumps' antigenic cross-reactivity and the protective effect of antibodies.

Inclusion Criteria:

1. Children aged 3-7 years old;
2. local resident children living at least 3 months;
3. physical health, has been vaccinated at least once a dose of MuV

Exclusion Criteria:

1. did not administer MuV;
2. refused to collect venous blood;
3. have been infected with mumps;
4. have serious illness or other reasons should not participate in the study after clinical evaluation

children aged 3-7 years who received as least one dose mumps-containing vaccine