Q Wu1, J Liu1, Y Wang1, Q Zhou1, X Wang1, Z Xuan1, L Zhang2, Y Gao3, B Chen3, Y Hu4. 1. Xuhui District Centre for Disease Control and Prevention, Shanghai, China. 2. School of Public Health, University of South China, Hunan Province, China. 3. Department of Epidemiology, China and Key Laboratory of Public Health Safety (Fudan University), School of Public Health, Fudan University, Ministry of Education, Shanghai, China. 4. Department of Epidemiology, China and Key Laboratory of Public Health Safety (Fudan University), School of Public Health, Fudan University, Ministry of Education, Shanghai, China. Electronic address: yhu@fudan.edu.cn.
Abstract
OBJECTIVES: Although administration of a second dose of varicella vaccine (2nd-dose VarV) to individuals who have previously received one-dose VarV has been recommended as a post-exposure prophylaxis (PEP) strategy for outbreak control, the effectiveness of this strategy remains unclear. We evaluated the vaccine effectiveness (VE) of 2nd-dose VarV as PEP among students involved in 129 varicella outbreaks in Shanghai, China from 2013 to 2016. METHODS: Students who had received one-dose VarV more than 5 years prior to varicella exposure were eligible to receive 2nd-dose VarV as PEP. We evaluated the VE using the following formula: VE = (1 - hazard ratio (HR)) × 100%. RESULTS: A total of 6762 students were eligible for 2nd-dose VarV, of whom 58.6% accepted PEP after varicella exposure. The adjusted VE of 2nd-dose VarV as PEP was 77% (95% confidence interval 64-85%). In addition, the adjusted VE of 2nd-dose VarV as PEP in affected classrooms with high vaccine uptake was higher than that in classrooms with lower vaccine uptake (87% vs. 69%). The adjusted VE was also higher in students who received 2nd-dose VarV within 3 days of exposure than those who received it more than 3 days post exposure (77% vs. 64%). CONCLUSIONS: These Results suggest that administration of 2nd-dose VarV as PEP is an appropriate intervention for outbreak control in countries where two-dose VarV has not been adopted.
OBJECTIVES: Although administration of a second dose of varicella vaccine (2nd-dose VarV) to individuals who have previously received one-dose VarV has been recommended as a post-exposure prophylaxis (PEP) strategy for outbreak control, the effectiveness of this strategy remains unclear. We evaluated the vaccine effectiveness (VE) of 2nd-dose VarV as PEP among students involved in 129 varicella outbreaks in Shanghai, China from 2013 to 2016. METHODS: Students who had received one-dose VarV more than 5 years prior to varicella exposure were eligible to receive 2nd-dose VarV as PEP. We evaluated the VE using the following formula: VE = (1 - hazard ratio (HR)) × 100%. RESULTS: A total of 6762 students were eligible for 2nd-dose VarV, of whom 58.6% accepted PEP after varicella exposure. The adjusted VE of 2nd-dose VarV as PEP was 77% (95% confidence interval 64-85%). In addition, the adjusted VE of 2nd-dose VarV as PEP in affected classrooms with high vaccine uptake was higher than that in classrooms with lower vaccine uptake (87% vs. 69%). The adjusted VE was also higher in students who received 2nd-dose VarV within 3 days of exposure than those who received it more than 3 days post exposure (77% vs. 64%). CONCLUSIONS: These Results suggest that administration of 2nd-dose VarV as PEP is an appropriate intervention for outbreak control in countries where two-dose VarV has not been adopted.