Effects of One-dose Varicella Vaccination on Disease Severity in Children during Outbreaks in Seoul, Korea.

BACKGROUND

In Korea, the incidence of varicella has increased despite the introduction of a universal one-dose vaccination for children aged 12-15 months in 2005. A previous study demonstrated that the vaccine effectiveness was insufficient to prevent against varicella. We assessed the effect of the varicella vaccination on disease severity.

METHODS

Epidemiologic investigation of varicella cases in Seoul metropolitan area from 2015 to 2017 were used. Varicella-related symptoms such as rash were determined by the clinical practitioners. Disease severity of patients was assessed by the number of skin lesions and divided into mild (≤ 50) and moderate (51-249) to severe (≥ 250). Unconditional logistic regression analysis was performed and age was controlled.

RESULTS

Among a total of 1,008 varicella cases reported, 869 cases were breakthrough cases and 139 were unvaccinated cases. The risk for occurrence of moderate-to-severe disease in the breakthrough group was 0.57 times less than that of the unvaccinated group.

CONCLUSION

These data suggest that national varicella vaccination may have a significant effect on attenuation of disease severity in children.