Abstract
ABSTRACT In Hong Kong, universal varicella vaccination was introduced in July 2014 with a two-dose schedule but the vaccines had been available in the private market since 1996. With data from varicella notification and surveys on immunization coverage, we used the screening method to estimate dose-specific varicella vaccine effectiveness (VE) among preschool children in Hong Kong before universal vaccination. We estimated the VE of one- and two-dose varicella vaccination against all notified varicella as 69.4% (95% confidence interval (95% CI) 69.5–71.2) and 93.4% (95% CI 91.7–94.7), respectively. We found that VE did not decrease with time since receipt. Varicella vaccine was more effective against complications (85.4% [95% CI 48.8–95.8] for one dose and 100% [95% CI –Inf to 100] for two doses) and against hospital admission (75.2% [95% CI 53.4–86.8] for one dose and 93.1% [95% CI 47.1–99.1] for two doses). Lower protection of one-dose varicella vaccine resulted in breakthrough varicella. Under universal vaccination, second-dose varicella vaccine (given as combined measles, mumps, rubella and varicella vaccine) was first scheduled for children when they reach primary one (about 6 years of age) and was recently advanced to 18 months of age. Shortening the interval between the first dose and second dose of varicella vaccination should reduce breakthrough varicella and outbreaks in preschool.
Highlights
Universal varicella vaccination (UVV) in Hong Kong was introduced in July 2014 for children born in 2013 and after with a twodose schedule at 12 months and around 6 years of age.[1]
Before the start of UVV, varicella vaccine was licensed for private market use in 1996 with no clear schedule and the first dose vaccination uptake gradually reached up to 50% among preschool children.[2]
Our vaccine effectiveness (VE) estimates are largely comparable to a recent metaanalysis of post-licensure VE studies[6] which showed that onedose varicella vaccine is moderately effective for preventing disease of any severity [81%] but two-dose varicella vaccine is highly effective at 98%
Summary
Universal varicella vaccination (UVV) in Hong Kong was introduced in July 2014 for children born in 2013 and after with a twodose schedule at 12 months and around 6 years of age (at the start of primary school).[1] Monovalent varicella vaccine (mVV) is provided as the first dose whilst combined measles, mumps, rubella, and varicella (MMRV) is provided as the second dose. Before the start of UVV, varicella vaccine was licensed for private market use in 1996 with no clear schedule and the first dose vaccination uptake gradually reached up to 50% among preschool children.[2] The private market was dominated by mVV from GSK, Sanofi, and MSD (Table 1). The extent to which this increase in varicella vaccination contributed to the change in epidemiology remains uncertain.[2]
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