Epidemiological characteristics of breakthrough varicella infection during varicella outbreaks in Shanghai, 2008–2014

Abstract

The outbreaks of varicella occurring in kindergartens and schools are increasingly notified in Shanghai despite the implementation of one-dose varicella vaccination. We analyzed surveillance data on the notified outbreaks of varicella in Minhang District of Shanghai during 2008-2014. A total of 13 511 varicella cases and 154 outbreaks involving 1558 (11·5%) cases were reported. Annual attack rates of outbreak-associated varicella in outbreak classes were 5·5%-12%. The mean age of the outbreak-associated cases was 8·6 ± 3·1 years. Among 1558 outbreak cases, 660 (42·4%) received one-dose varicella vaccine previously. The proportions of breakthrough varicella infection during outbreaks ranged from 21·5% in 2008 to 86·1% in 2014. Annual breakthrough infection rates in outbreak classes ranged from 5·4% to 7·4%. Breakthrough cases as index cases results in 9·7% of outbreaks, and the average duration of outbreaks was significantly longer in vaccinated cases as index cases than in unvaccinated cases as index cases (11·3 ± 5·8 days vs. 8·6 ± 6·1 days, P < 0·05). The mean time of breakthrough infection since vaccination was 6·2 ± 2·3 years (range 0·6-13·4 years). One-dose varicella vaccination cannot prevent the varicella outbreaks in kindergartens and schools. A second dose of varicella vaccine should be recommended for children.

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

“…This study found that the proportion of BV cases among all outbreak-related cases was 56.5%, higher than the results of a population-based survey (22%) (Chaves et al, 2008), but within the range of several outbreak-based studies (42-76%) (Leung et al, 2015;Zhang et al, 2014b;Zhu et al, 2017). It was also found that the proportion of BV cases showed an increasing trend from 30.4% in 2008 to 85.7% in 2017.…”

“…Previous studies have shown that single-dose VarV performed satisfactorily in China, with vaccine effectiveness (VE) between 50.3% and 83.9% (Fu et al, 2010;Pan et al, 2018;Wang et al, 2013). However, in some cities with high economic productivity in China, such as Beijing and Shanghai, school outbreaks continue to occur despite high VarV coverage (Fu et al, 2015;Lu et al, 2012;Suo et al, 2017;Zhu et al, 2017). To contain varicella outbreaks, the administration of VarV has been recommended as a post-exposure prophylaxis (PEP) strategy in Chinese metropolitan cities, including Beijing (2006), Guangzhou (2012), and Shanghai (2013) (Cao et al, 2018;Li, 2013;Ma et al, 2009).…”

A Centralized Outbreak of Varicella among Children Attending Preschool in Suzhou, China

“…Although great achievement had been made in reducing varicella incidence, outbreaks continued to be reported, especially in preschools, schools, etc. [8][9][10].…”

Factors Influencing the Size and Duration of School Varicella Outbreaks in Shanghai, China, in the Era of Voluntary Single-Dose Vaccination

“…In China, the varicella vaccine (VarV) was introduced in 1998 as a voluntary single-dose regimen for children aged ≥12 months. Although single-dose VarV coverage reached up to 90% of schoolchildren aged 3–14 years, outbreaks remained frequent in Shanghai from 2008 to 2014 [1]. The proportion of vaccinated cases, also known as breakthrough varicella (BV) cases, rose from 21% in 2008 to 86.1% in 2014 [1].…”

“…Although single-dose VarV coverage reached up to 90% of schoolchildren aged 3–14 years, outbreaks remained frequent in Shanghai from 2008 to 2014 [1]. The proportion of vaccinated cases, also known as breakthrough varicella (BV) cases, rose from 21% in 2008 to 86.1% in 2014 [1]. Although the symptoms of BV are mild, infectious BV cases can contribute to spread of outbreaks [1, 2].…”