In 2016, a mumps outbreak occurred in a Chinese primary school with a high vaccination coverage among the student population. An unmatched case-control research was carried out to identify risk variables leading to this epidemic, and a retrospective cohort analysis was carried out to assess the efficacy of mumps-containing vaccination (MuCV). During the epidemic, 97 cases were recorded, with an overall attack rate of 8.2 percent. Ninety percent of pupils with verified vaccination status had received at least one dose of MuCV. During the pandemic era, patients were more likely than non-cases to report using the school bus. The two-dose MuCV vaccine had a greater VE than the one-dose MuCV vaccine. The protection provided by both one-dose and two-dose MuCV decreased with time, falling from 82 percent among those vaccinated within 5 years to 41 percent among those vaccinated more than 10 years previously for one-dose VE and from 90 percent to 25 percent over the same time period for two-dose VE. 

Despite widespread immunization with a single dose of MuCV, researchers discovered that mumps outbreaks can occur in schools. Although the VE of both two-dose and one-dose MuCV decreases with time, the total VE of two-dose MuCV was greater than that of one-dose MuCV. As a result, a two-dose MuCV regimen delivered through regular services is likely required to prevent mumps outbreaks in China.

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Reference:https://www.tandfonline.com/doi/full/10.1080/21645515.2019.1581526