Abstract
National one-dose varicella vaccination at 12 months of age was implemented in Taiwan since 2004.Our study aimed to evaluate breakthrough varicella (BV) in post-vaccine era and its associated risk factors. We retrospectively identified children vaccinated against varicella between 12–23 months of age during 2004–2008. Their vaccination information was extracted from the national vaccination registry system and linked to the 2004–2014 National Health Insurance database. BV was defined as a diagnosis of varicella (ICD-9-CM codes 052 and 052.0–052.9) beyond 42 days post-vaccination. Multiple Cox regression model was used to identify risk factors for BV. Among 932,874 enrolled vaccinees, 26,446 (2.8%) had BV and 219 (0.024%) required hospitalization over the study period. Varicella incidence declined from 4.71 per 1000 person-year (PY) in 2004 to 0.81/1000 PY in 2014. BV incidence decreased from 3.90/1000 PY at first year to 1.94/1000 PY at 11th year after vaccination. Females had a lower risk for BV than males (hazard ratio [HR] 0.85, 95% CI, 0.83–0.87); Varivax® recipients had a lower risk for BV than Varilrix® recipients (HR 0.75, 95% CI, 0.72–0.78). Our study showed the incidence of varicella, BV and varicella-related hospitalizations in Taiwan were kept low in post-vaccine era.
Highlights
Varicella vaccine was first developed in 1974 and is currently the most effective method to prevent varicella in children
No robust evaluation of the effectiveness of the universal varicella vaccination program and the incidence of breakthrough varicella (BV) has yet been performed since the start of Universal varicella vaccination (UVV)
The annual number of varicella patients in all age groups recorded in the National Health Insurance (NHI) database decreased from 106,913 in 2004 to 18,960 in 2014 (Fig. 1), which constitutes a reduction of more than 80% of all varicella patients during the 11-year routine varicella vaccination program
Summary
Varicella vaccine was first developed in 1974 and is currently the most effective method to prevent varicella in children. Universal varicella vaccination (UVV) with one dose at 12 months of age was not implemented at the national level until 2004. In Taiwan, a sero-epidemiological survey in school children in 2013 reported that only approximately 64.1% of children in primary school (aged 7–12 years) remained seropositive for varicella-zoster virus using an indirect chemiluminescence immunoassay (Liaison, DiaSorin, Italy)[6]. This result could be due to the low sensitivity of commercial serological assays in picking up vaccine-induced immunity[7,8].
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