Single-dose varicella vaccine effectiveness in school settings in China☆
Introduction
Varicella (chickenpox) is a highly contagious disease caused by infection with varicella zoster virus (VZV), and is characterized by a generalized pruritic vesicular rash. Although varicella is usually self-limiting and resolves within a week, severe complications, including death, can occur [1].
Varicella vaccines are now widely available as the most effective measure for prevention and control of varicella. In China, varicella vaccine first became available in 1998. Five vaccines are currently licensed in China for single dose use in persons 12 months and older: Varilrix® (GlaxoSmithKline) and four domestic vaccines (Baike, Changsheng, Keygen, and Shanghai). The five varicella vaccines have similar concentrations of Oka strain VZV: >1995 plaque forming unit/dose (0.5 mL) in Varilrix, and >2000 plaque forming unit/dose (0.5 ml) in the domestic vaccines. The five vaccines have the same temperature requirement (2–8 °C) for cold-chain storage and transportation. Currently, varicella vaccines are only available for private purchase in China and vaccination coverage varies substantially by regional level of economic development [2], [3], [4], [5]. Although their immunogenicity and safety have been assessed previously in randomized clinical trials [6], [7], [8], [9], [10], [11], [12], [13], the effectiveness of these vaccines in China have not yet been fully examined in school settings, the most likely places for intense varicella exposure as a consequence of decreasing family sizes in China [14]. A matched case–control study was carried out in schools and daycares to examine the post-licensure effectiveness of varicella vaccines in school settings in Shandong Province, China.
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Study population
The China Center for Disease Control and Prevention (CDC) and Tai’an CDC conducted a case–control study in schools and daycare centers in five counties of Tai’an prefecture, Shandong province, from 3/2010 to 6/2011. A case of varicella was defined as an acute generalized maculopapulovesicular rash without other apparent cause [15]. Breakthrough varicella was defined as a case that developed >42 days after vaccination [15]. Although varicella was not a notifiable disease in Tai’an prefecture
Characteristics of the study participants
There were a total of 180 cases reported from 44 schools and day cares and 679 controls enrolled. Half (434, 50.5%) of the 859 participants were female. The majority of participants were elementary school students (589, 68.6%) with a mean age of 7.3 years (range: 1.3–12.4). Five participants reported having underlying medical conditions of asthma and eczema. More than half of the cases (97/180) reported a VZV exposure, 93 (95.9%) of which were at school. Of the 250 (29.1%) vaccinated cases and
Discussion
Our study showed that single-dose varicella vaccination in China was highly effective in preventing varicella in school settings. With varicella vaccine currently only available in China in the private sector, we found moderate varicella vaccination coverage had been achieved, although there was substantial variation across schools. Our study is the first to examine the effectiveness of two varicella vaccines (Baike and Changsheng) that are produced in China., which appear to offer comparable
Acknowledgments
We highly appreciate the help from the local health departments, school nurses, and teachers in case finding and control enrollment. We also are indebted to the children and their parents/guardians for their participation and cooperation.
Conflict of interest statement: The authors have no conflicts of interest or funding to disclose.
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The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention, U.S. Department of Health and Human Services.