Impact of Varicella Immunization and Public Health and Social Measures on Varicella Incidence: Insights from Surveillance Data in Shanghai, 2013-2022

Abstract

To evaluate the impact of a two-dose VarV program on varicella incidence among the whole population, considering the influence of public health and social measures (PHSMs), we extracted surveillance data on varicella cases during 2013-2022 in Minhang, Shanghai. Then, we estimated the incidence trend of varicella through interrupted time-series analyses and quantified the impact of the immunization program and PHSMs using Serfling regression. We also explored the associations between PHSMs and varicella cases. The implementation of the two-dose VarV strategy was followed by a significant decrease in varicella incidence (-1.84% per month). After one year of the program, varicella incidence was estimated at a 45.25% reduction, which was higher in children (59.12% and 54.09%) than in adults (19.49%). The decrease attributed to PHSMs was 31.26% during 2020-2022, and school closing was identified as the most relevant PHSM (b = -8.03 cases, r = -0.67 with a 1-week lag). These findings indicate that the two-dose immunization program has more effectively reduced the varicella incidence compared with the one-dose vaccine, and interventions like school closings are also encouraged to serve as supplementary measures to prevent varicella epidemics.

Keywords: PHSMs; incidence; vaccination program; varicella.

Figure 1

Association of the implementation of the two-dose VarV strategy and PHSMs with the monthly incidence of varicella per 100,000 inhabitants in Minhang District, 2013–2022. The blue line represents the monthly varicella incidence in Minhang, Shanghai, during 2013–2022. The orange slope lines are incidence trends estimated via segmented regression. The orange shading areas are the 95% CIs estimated via segmented regression. The dashed vertical lines represent the transition periods, including the two-dose VarV strategy implementation (November–December 2017) and the first wave of PHSM implementation (January 2020). The dotted vertical lines represent the inclusion of the two-dose VarV strategy in the local immunization program (August 2018) and the second wave of PHSM implementation (March 2022). PHSMs: public health and social measures; VarV: varicella vaccine.

Figure 2

Reduction in the monthly incidence of varicella in Minhang District, 2018–2022. (a) Blue line indicates monthly incidence of varicella in 2018. Red line indicates fitted data estimated using Serfling regression. Green shadows indicate the reduction between actual incidence and fitted data, which was a significant reduction of 20.90% (t = −3.14, p < 0.001). (b) The reduction between actual incidence in 2019 and fitted data was significant, which was 45.25% (t = −13.30, p < 0.001). (c) Orange line indicates predicted incidence in 2020–2022 on the assumption that identical effect was caused by the two-dose VarV strategy in 2019. A total reduction of 76.51% was observed during 2020–2022, in which 31.26% was attributed to PHSMs (orange shadows). PHSMs: public health and social measures.

Figure 3

Results of cross-correlation Spearman rank correlation between PHSMs and the number of weekly varicella cases in Minhang District, 2020–2022. Each figure denotes the Spearman rank correlation coefficient between the PHSM in the row and the number of varicella cases at time-shifted intervals of 0–10 weeks. Only significant results are presented (p < 0.05). PHSMs: public health and social measures.