Waning immunity and potential asymptomatic infection in 3–7 years old children who received one dose of measles-mumps-rubella vaccine: A 4-year prospective study

Mumps outbreaks in adolescents who received two doses of measles-mumps-rubella vaccine (MMR) during childhood have been reported worldwide. In China, one dose of MMR administered in children aged among 18–24 months has a limited effect on the mumps epidemic. There are limited prospective studies evaluating the mumps immunity profile of children aged 3–7 years who received one dose of MMR. This study aimed to describe mumps immunity profile over a span of 4-years in kindergarten and primary school children. An observational, prospective study on one-dose MMR in children aged 3–7 years who underwent blood sample collection in 2015, 2016, and 2018 was conducted from 2015 to 2018. The seropositivity and geometric mean concentration of mumps IgG antibodies over time were analyzed. A total of 3346 eligible children aged 3–7 years who underwent three rounds of blood sample collection were included. The overall seropositivity (79.6%) in 2015 was significantly higher than those recorded in 2016 (73.1%) and 2018 (71.4%). Approximately 11.6–15.9% of the participants were seropositive for mumps in 2015, and converted to negative in 2016. Meanwhile, 11.1–14.6% of the participants were seropositive for mumps in 2016, and the results converted to negative in 2018. Over 6.1–7.4% of the participants had asymptomatic infection from 2015 to 2016, while 9.0–9.9% of the participants were infected without clinical symptoms from 2016 to 2018. Kindergarten and primary school children who only received one dose of MMR were at higher risk of developing mumps. Waning immunity, seronegative conversion, and asymptomatic infection coexist in children who received one dose MMR. Determining the optimal age for administering the second dose of MMR in children should be prioritized to improve the control and prevention of mumps in China.