A Varicella Outbreak in a Primary School, Taiwan, 2010

Sung-Hsi Wei, Chiung-Hui Tseng, Du-Lin Ling,Chih-Tsung Tu, Horng-Ying Chiou, Tsuey-Feng Lee

2011 Vol.27 NO.7

Correspondence Author: Sung-Hsi Wei


Varicella is a vaccine preventable disease and its vaccination was proceeded in some cities and areas in Taiwan since 1998. This report describes a cluster infection of varicella in a primary school.
From March 1 to June 30, 2010, school teachers and medical care staffs recorded varicella infection of the students. Varicella vaccination status was checked in National immunization information system (NIIS) and varicella infection status of this school prior to this outbreak was inquired in NIIS and Notifiable Disease Reporting System. Telephone interview with the patients and their parents were also conducted to understand the severity of the disease, clinical symptoms and duration time. The infected students were home isolated for at least one week until the vesicles healed. Disinfection was proceeded and varicella prevention education was provided to prevent further exposure.
There were 742 students in this school; 28 (3.8%) were infected with varicella and 401 (54%) had received varicella vaccine prior to this outbreak. Except 6 students, all other students received varicella vaccine at least 5 years ago before outbreak. During this event, 23 students were infected and the attack rate was 3.2%; 10 of the 23 patients had received varicella vaccine. The efficacy of varicella vaccination calculated through this event was 40%. Compared to patients without immunization, patients previously vaccinated were less likely to develop moderate or severe disease (odds ratio: 0.110, confidence interval: 0.009-1.013, p=0.036) and the duration time was shorter (odds ratio: 0.021, confidence interval: 0.000-0.352, p<0.001).
This report revealed a varicella outbreak in a school where most students received vaccination for at least 5 years ago and single dose of varicella vaccine may be insufficient in long term protection from varicella infection. However, previous varicella vaccination may help in decreasing the severity of illness and duration time.