Estimating the basic reproductive number of varicella in South Korea incorporating social contact patterns and seroprevalence

Abstract

Varicella, which is caused by the varicella zoster virus (VZV), is a common infectious disease affecting children. Varicella vaccines have been used for decades; however, vaccination policies vary across countries because of differences in VZV epidemiology. The basic reproductive number $${{\rm{R}}_0}$$ a transmissibility measure parameter, also differs from country to country. In this study $${{\rm{R}}_0}$$ for varicella was estimated in South Korea using the contact rate matrix derived from averaged POLYMOD contact data, the Korean population, and proportionality factor fitted to the Korean VZV seroprevalence $${{\rm{R}}_0}$$ for varicella in South Korea was estimated to be 5.67 (95% CI: 5.33, 6.33). Therefore, to reach the herd immunity threshold, the critical vaccine coverage should be greater than 82.4% with a perfect vaccine, or the primary vaccine failure proportion should be less than 17.6% with 100% coverage. Because of the relatively low seroconversion rate and rapidly waning immunity after one-dose vaccination in South Korea, the herd immunity threshold is difficult to attain with only a one-dose vaccine. Two doses of vaccination may be necessary to effectively interrupt varicella transmission and maintain herd immunity in South Korea. The study results can help guide the decision-making on an effective varicella vaccination policy in South Korea.

Keywords

• varicella
• contact patterns
• basic reproductive number
• herd immunity threshold
• korea