Varicella-zoster virus (VZV) is a highly contagious herpesvirus that can cause varicella (chickenpox) in children and herpes zoster (shingles) in adults, and most people would become infected by mid-adulthood in the absence of a varicella vaccination program (1). Epidemiological data on varicella is needed before the vaccine can be included into China’s Expanded Program on Immunization (EPI).
The timing of administering the vaccination is crucial for controlling the spread of varicella, but the mainland of China lacks a uniform schedule for these vaccinations. This study compared Beijing and Ningbo of Zhejiang Province to analyze the differences in varicella incidence when compared to different vaccination schedules for the first dose and different coverage of the second dose.
After 2007, Beijing and Ningbo have required the compulsory reporting of varicella incidence through the National Notifiable Diseases Reporting System (NNDRS) of the mainland of China. The epidemiological data from regions where compulsory reporting had been implemented provide some valuable information, and all the data in this paper is from the NNDRS (2007–2018).
Beijing and Ningbo are developed areas in the mainland of China. The immunization program and infectious disease surveillance of the two cities are well organized and their data on varicella is comparatively higher quality within China (2-4). A two dose immunization schedule is recommended in the two cities with little difference for the first dose. The first dose of vaccine was set to be administered at 18 months of age in Beijing starting in 2007 and 12–18 months in Ningbo starting from 2012. The second dose was set to be administered at 4 years of age in Beijing since 2012 and Ningbo since 2014. The varicella inoculation rate for the first dose is higher than the second dose and the inoculation rate for Beijing is higher than Ningbo. (Figure 1)Figure 1. The inoculation rate of different dose of varicella vaccines in Beijing and Ningbo city, China, 2017. Beijing-1 and Ningbo-1 is the inoculation rate of the first dose of varicella vaccines in Beijng and Ningbo, Beijing-2 and Ningbo-2 is the inoculation rate of the second dose of varicella vaccines in Beijing and Ningbo.
There is a noticeable difference in varicella incidence in age group 1 (12 to 24 months) in the two cities with the incidence in Beijing being much higher than that of Ningbo. In Beijing, the incidence in age group 1 initially increased and then declined slightly, but Ningbo had a relatively low incidence without significant changes. (Figure 2)Figure 2. The incidence of varicella by age group from 0 to 15 after taking the vaccination in Beijing and Ningbo city, China, 2012–2018. The incidence from 0 to 9 represents each year age group. The incidence of 10 and 15 age group represents the incidence of 10–14 years and 15–19 years, respectively.
After the implementation of the two-dose schedule in Beijing from 2012, the total population incidence decreased significantly but increased slightly after 2016. Ningbo also showed decreases after introducing the second dose of vaccine in 2014 but had dramatic increases after 2016.
Further analysis of the incidence of the sub-age group 0 years old to 15 years old in Ningbo reveals a prominent increase for the age group of 9 years old to 10 years old (from 9 years old to 14 years old) after 2014 (Figure 2), and the peak incidence of Ningbo is backward from 4–8 years old in 2012, to 9–13 years old in 2018 (Figure 3).