Despite the fact that a varicella vaccination has been available in the commercial sector in China since 1998, varicella outbreaks and breakthrough varicella (BV) continue to occur. Four varicella outbreaks with high BV rates occurred in four schools in Lu’an, raising local public health authorities’ concerns about the varicella vaccine. As a result, the researchers undertook this study to assess varicella vaccine effectiveness (VE) and identify potential risk factors for BV. This was a three-stage investigation. First, in each school, a retrospective cohort analysis was conducted to assess the VEs of varicella vaccination during outbreaks. Second, a descriptive epidemiological method was utilised to describe the four outbreaks and compare the clinical characteristics of BV cases and unvaccinated varicella cases. In the third stage of the study, they conducted an unmatched case-control analysis to investigate the risk factors linked with BV. A total of 199 cases were discovered over four outbreaks, with an overall attack rate of 14%. The total VEs among the four outbreaks ranged from 19% to 69%, while the VE against moderate or severe varicella ranged from 74% to 90%. Children who had been vaccinated more than six years before the epidemic had a higher chance of having BV than those who had been vaccinated within the last six years.

The overall VE was insufficient to protect against varicella infection, and the VE for moderate to severe varicella infection was only modest. The symptoms of BV were often milder than those of spontaneous varicella infection.

Reference: https://www.tandfonline.com/doi/full/10.1080/21645515.2019.1704574