Zhijuan Cao1, Daoyong Chen2, Yanji Yang3, Donglan Zhang4. 1. Shanghai First Maternity and Infant Hospital, Tongji University School of Medicine, 2699 West Gaoke Rd, Pudong New District, Shanghai 201204, China. Electronic address: zhijuancao@tongji.edu.cn. 2. Hongkou Center for Disease Control and Prevention, 197 Changyang Rd, Hongkou District, Shanghai 200082, China. 3. Hongkou Center for Disease Control and Prevention, 197 Changyang Rd, Hongkou District, Shanghai 200082, China. Electronic address: shineyung@hotmail.com. 4. Department of Health Policy and Management, College of Public Health, University of Georgia, 100 Foster Road, 205D Wright Hall, Athens, GA 30602, USA. Electronic address: dzhang@uga.edu.
Abstract
OBJECTIVES: To evaluate the effectiveness of post-exposure prophylaxis conducted during varicella outbreaks among students in Shanghai. METHODS: Surveillance data were collected from September 1, 2013 to December 31, 2016 involving 3524 susceptible students in 109 primary and middle school classes where emergency vaccinations (EVs) had been administered. Students were divided into two groups according to their prior vaccination (PV) varicella vaccine status. A secondary attack rate was used to compare EV and non-EV groups using a chi-squared test. Stratification analyses were performed, adjusting for the EV administration date, the vaccination coverage rate, and the number of cases prior to the EV. RESULTS: The effectiveness rate was 92.2% (95% confidence interval (CI): 37.1-99.0%) when EV was applied within 3 days following the outbreak onset date, and 95.2% (95% CI: 79.9-98.8%) when vaccination coverage was ≥80% among students with PV. When students with PV received an EV for varicella within 3 days, the effectiveness rate was 100%. CONCLUSIONS: EV showed high protective effectiveness for varicella during outbreaks, especially if administered within 3 days of an outbreak and in conjunction with a high coverage rate.
OBJECTIVES: To evaluate the effectiveness of post-exposure prophylaxis conducted during varicella outbreaks among students in Shanghai. METHODS: Surveillance data were collected from September 1, 2013 to December 31, 2016 involving 3524 susceptible students in 109 primary and middle school classes where emergency vaccinations (EVs) had been administered. Students were divided into two groups according to their prior vaccination (PV) varicella vaccine status. A secondary attack rate was used to compare EV and non-EV groups using a chi-squared test. Stratification analyses were performed, adjusting for the EV administration date, the vaccination coverage rate, and the number of cases prior to the EV. RESULTS: The effectiveness rate was 92.2% (95% confidence interval (CI): 37.1-99.0%) when EV was applied within 3 days following the outbreak onset date, and 95.2% (95% CI: 79.9-98.8%) when vaccination coverage was ≥80% among students with PV. When students with PV received an EV for varicella within 3 days, the effectiveness rate was 100%. CONCLUSIONS:EV showed high protective effectiveness for varicella during outbreaks, especially if administered within 3 days of an outbreak and in conjunction with a high coverage rate.