Severe and Complicated Varicella and Associated Genotypes 10 Years After Introduction of a One-Dose Varicella Vaccine Program

Abstract

Background. This national, sentinel prospective study aimed to identify children with severe hospitalized varicella, despite availability of universal 1-dose vaccination since 2005, and determine associations between virus genotypes and disease severity. Methods. Children with varicella or zoster from 5 Paediatric Active Enhanced Disease Surveillance hospitals were enrolled. Lesions were swabbed for genotyping. Associations with disease severity were analyzed using multiple regression. Results. From 2007 to 2015, 327 children with confirmed varicella (n = 238) or zoster (n = 89) were enrolled. Two hundred three (62%) were immunocompetent children; including 5 of 8 children who required intensive care unit management. Eighteen percent (36 of 203) of immunocompetent children had been previously vaccinated. Vaccinated children aged >18 months were less likely to have severe disease (9%; 5 of 56) than unvaccinated children (21%; 21 of 100; P = .05). Three of 126 children who had virus genotyping (2 immunocompromised) had varicella (n = 2) or zoster (n = 2) due to the Oka/vaccine strain. European origin clades predominated and were independently associated with more severe disease (odds ratio = 3.2; 95% confidence interval, 1.1- 9.5; P = .04). Conclusions. Severe hospitalized varicella still occurs with a 1-dose varicella program, although predominantly in unvaccinated children. Most 1-dose vaccine recipients were protected against severe disease. Viral genotyping in complex hospitalized cases is important to assist in monitoring disease due to Oka-vaccine strain.