Varicella breakthrough infection and effectiveness of 2-dose varicella vaccine in China

2-dose varicella vaccination has been available in Ningbo city, China since 2014 in the private sector. This study aimed to evaluate the breakthrough varicella infection rate, and to examine overall and incremental effectiveness of 2-dose varicella vaccination among Chinese children.

A retrospective investigation was done among native children born from 2008 to 2013 in active surveillance area in Ningbo, China. Between 2009 and 2016, demographic information and data on varicella vaccination were collected by Ningbo's Immunization Information System, and information of varicella infections were obtained from China Information System for Disease Control and Prevention. The logistic regression was conducted to estimate varicella vaccine effectiveness (VE).

A total of 107,324 local children were enrolled in the cohort analysis and 95.11% of these children with no varicella disease history received at least 1-dose varicella vaccine from 2009 to 2016. The total breakthrough varicella infection rate (BVR) was 0.37% for all the vaccinated children and 0.04% for 2-dose vaccination. The annual BVR ranged from 0.01% to 0.49% for 1-dose of varicella vaccine and from 0.01% to 0.02% for 2-dose. The infection rates both in the unvaccinated children and the 1-dose children were decreasing after 2-dose vaccination implemented in 2014 (Unvaccinated: P < 0.001 for trend; 1-dose: P = 0.003 for trend). The VE against all varicella was 50.3% (95% CI: 39.8%-59.0%) for 1-dose (P < 0.001) and 98.7% (95% CI: 98.1%-99.1%) for 2-dose (P < 0.001), and the incremental VE was 97.4% (95% CI: 96.2%-98.2%) compared with 1-dose (P < 0.001).

The 2-dose regimen provided excellent protection to prevent all varicella, and the universal 2-dose regimen of varicella vaccine should be recommended to prevent the varicella disease among children in China.