Severe and Complicated Varicella and Associated Genotypes 10 Years After Introduction of a One-Dose Varicella Vaccine
Helen S Marshall1,2, Michelle Clarke1,2, Christine Heath1
1Women's and Children's Health Network, Adelaide, Australia.
Insights
Severe varicella (chickenpox) hospitalizations occur in children despite vaccination, primarily in unvaccinated individuals. However, the 1-dose varicella vaccine effectively protects most recipients against severe illness.
Area of Science:
- Pediatric Infectious Diseases
- Vaccinology
- Virology
Background:
- Severe varicella (chickenpox) hospitalizations persist in children despite widespread 1-dose vaccination since 2005.
- Understanding factors contributing to severe varicella in vaccinated and unvaccinated children is crucial.
Purpose of the Study:
- To identify children with severe hospitalized varicella.
- To determine associations between varicella virus genotypes and disease severity in children.
Main Methods:
- Prospective surveillance study enrolling children with varicella or zoster from sentinel hospitals.
- Lesion swabbing for viral genotyping and analysis of disease severity using multiple regression.
Main Results:
- 327 children were enrolled (238 varicella, 89 zoster) between 2007-2015.
- Vaccinated children over 18 months were less likely to experience severe disease (9%) compared to unvaccinated children (21%).
- European varicella virus clades were associated with increased disease severity (OR=3.2).
Conclusions:
- A 1-dose varicella vaccination program reduces, but does not eliminate, severe varicella hospitalizations in children.
- The Oka/vaccine strain was rarely detected in severe cases.
- Viral genotyping is valuable for monitoring varicella strains in hospitalized children.
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.
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