Single-dose varicella vaccine effectiveness in Brazil: A case-control study

Publication date: 25 January 2018
Source:Vaccine, Volume 36, Issue 4
Author(s): Ana Lucia Andrade, Maria Aparecida da Silva Vieira, Ruth Minamisava, Cristiana Maria Toscano, Menira Borges de Lima Souza, Fabíola Fiaccadori, Cristina Adelaide Figueiredo, Suely Pires Curti, Maria Lígia Bacciotte Ramos Nerger, Ana Luiza Bierrenbach
BackgroundVaricella vaccine was introduced into the Brazilian Immunization Program in October 2013, as a single-dose schedule administered at 15 months of age. Its effectiveness had not yet been assessed in the country.MethodsA matched case-control study was carried out in São Paulo and Goiânia (Southeast and Midwest regions, respectively), Brazil. Suspected cases, were identified through a prospective surveillance established in the study sites. All cases had specimens from skin lesion collected for molecular laboratory testing. Cases were confirmed by either clinical or PCR of skin lesions and classified as mild, moderate, and severe disease.Two neighborhood controls were selected for each case. Cases and controls were aged 15–32 months and interviewed at home. Evidence of prior vaccination was obtained from vaccination cards. Univariate and multivariate logistic regression models were used, and odds ratio and its respective 95% confidence intervals were estimated. Vaccine effectiveness was estimated by comparing de odds of having received varicella vaccine among cases and controls.ResultsA total of 168 cases and 301 controls were enrolled. Moderate and severe illness, was found in 33.3% and 9.9% of the cases. Effectiveness of a single dose varicella vaccine was 86% (95%CI 72–92%) against disease of any severity and 93% (95%CI 82–97%) against moderate and severe disease. Out of 168 cases, 81.8% had positive PCR results for wild-type strains, and 22.0% were breakthrough varicella cases. Breakthrough cases were milder compared to non-breakthrough cases (p < .001).ConclusionsEffectiveness of single dose varicella vaccine in Brazil is comparable to that in other countries where breakthrough varicella cases have also been found to occur. The goal of the varicella vaccination program, along with disease burden and affordability should be taken into consideration when considering the adoption of a second dose of varicella vaccine into national immunization programs.



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