Comparative varicella vaccine effectiveness during outbreaks in day-care centres

Routine varicella vaccination for children >11 months was introduced in Germany in 2004 with three different vaccine brands available. In 2008 and 2009, we investigated seven varicella outbreaks in day-care centres (DCC).

Varicella disease and vaccination status of 1084 children was reviewed to evaluate vaccination coverage (VC), brand-specific varicella vaccine effectiveness (VE), and risk factors of breakthrough varicella (BV, >42 days after vaccination). A case was defined as a child with acute onset of varicella attending one of the respective DCC at the time of outbreak. Children with a previous history of varicella, age<11 months, vaccinated at age<11 months or <42 days before disease onset or during the outbreak were excluded from VE and BV risk factors analyses (adjusted for gender, age and DCC).

Of 631 children with available vaccination information, 392 (62%) were vaccinated at least once. Overall VE among 352 children eligible was 71% (95% confidence interval (CI) 57-81, p<0.001) and differed significantly by disease severity and number of doses administered. Risk for BV was higher for 1 dose of Varilrix (RR=2.8, 95%CI 1.0-7.8, p=0.05) or Priorix-Tetra (RR=2.4, 95%CI 0.7-8.3, p=0.18) but lower for 2 doses of Priorix-Tetra (RR=0.5, 95%CI 0.1-2.7, p=0.41) than for 1 dose of Varivax.

Enhanced efforts to increase VC in Germany and 2 doses varicella vaccine might be successful to reduce the risk for BV. The evidence that VE and risk of BV are associated with vaccine brand needs further investigation.