Varicella outbreak trends in school settings during the voluntary single-dose vaccine era from 2006 to 2017 in Shanghai, China

Abstract

To investigate varicella outbreak trends among schoolchildren during the voluntary singledose varicella vaccine (VarV) era in Shanghai, China. Methods: Trends in school varicella outbreaks from 2006 to 2017 were assessed using joinpoint regression models. The impacts of changes in single-dose VarV coverage among schoolchildren and implementation of post-exposure prophylaxis (PEP) strategies on outbreak trends were further analyzed. Results: In total, 265 varicella outbreaks involving 3263 cases were reported in Shanghai from 2006 to 2017. The number of outbreaks showed an increasing trend from 2006 to 2017 (t = 2.62, p = 0.026), especially in kindergartens. The proportion of breakthrough varicella cases among all outbreak-related cases showed an increasing trend from 30.4% in 2008 to 85.7% in 2017 (t = 7.45, p < 0.001). Single-dose VarV coverage among schoolchildren was 88.1%, and showed a significant increase from the 1996 to the 2008 birth cohorts, followed by a non-significant decline from the 2008 to the 2014 birth cohorts. During school outbreaks in which PEP campaigns were conducted, the varicella attack rate was significantly lower than those in outbreaks without PEP campaigns (1.2% vs. 1.4%; Chi-square = 23.35, p < 0.001). Conclusions: Even with high coverage, single-dose VarV is insufficient to prevent school outbreaks. The administration of VarV as PEP is an appropriate intervention for varicella outbreak control prior to implementing a two-dose VarV schedule.

Changes in epidemiological features of vaccine preventable infectious diseases among three eras of national vaccination strategies from 1953 to 2018 in Shanghai, China

“…However, the top two infectious diseases with the highest yearly incidence are varicella and HFMD, which are also highly prevalent among children. In childcare institutions and schools, outbreaks of varicella [10] and HFMD occur frequently. In addition, both diseases are associated with complications, posing as public health burdens and should not be ignored [22] .…”

“…Since the introduction of the first vaccination plan in 1978, incidence of most VPDs has remained under control. However, several outbreaks have occurred in recent decades and have affected Shanghai, including a hepatitis A epidemic in 1987 (a result of ingestion of infected blood clams) [7] , rubella in 1993 [8] , and additionally, persistent outbreaks of varicella, hand, foot, and mouth disease (HFMD) and influenza in the last two decades [9] , [10] . As one of the leading cities in public health quality, other Chinese cities look to Shanghai for adoption of health policies.…”

Characteristics of within-household varicella transmission events associated with school outbreaks in Shanghai, China, 2009–2018

“…A voluntary single-dose varicella vaccine (VarV) schedule has been recommended in Shanghai since 1998 for children aged ≥12 months, and routine two-dose vaccination was included in the immunisation programme in August 2018 for children aged 1–4 years [4]. Although single-dose VarV coverage among schoolchildren was 88%, school outbreaks continued to occur frequently in Shanghai from 2006 to 2017 [4]. This study aimed to investigate the characteristics of varicella cases in households and the modes of varicella transmission between school and household settings in Shanghai.…”

“…Among the 278 households studied, about half of within-household transmission events occurred between children and about 40% of within-household transmission events occurred between children and adults. The lower rate of transmission between children is likely due to the high proportion of single-child households (86.0–94.2%) [4]. However, schoolchildren cases tend to have higher visitation rates than adults [5], which may contribute to the underestimation of within-household transmission between children and adults.…”

“…In addition, our study confirmed that nearly 30% of household varicella transmission events were caused by cases infected during school outbreaks, and that 7.6% of school outbreaks were initiated from household-transmitted varicella. With the implementation of China's two-child policy, the proportion of schoolchildren with siblings is increasing [4], which may increase the risk of varicella transmission between schools and households. Therefore, ‘school-household-school’ transmission makes school outbreak control more difficult.…”