Varicella rates among unvaccinated and one-dose vaccinated healthy children in Izmir, Turkey.

OBJECTIVES: We aimed to determine the rate of breakthrough varicella in Turkey, a country with low varicella vaccination coverage. METHODS: This study was conducted between April 2008 and March 2009 at the Well-Child Clinic at Ege University and pediatricians' offices. We collected information on vaccination status and varicella infection using a questionnaire. In order to elicit more details about the severity of illness, we interviewed all parents and reviewed the clinician records. Vaccination status was verified from the medical records or vaccination cards with dates. RESULTS: A total of 2802 children were evaluated. Of these, 1683 had been vaccinated with a single dose of varicella vaccine and 1119 were unvaccinated. Among vaccinated children, 466 (27.7%) had breakthrough varicella. Vaccinated children tended to have mild varicella. However, about 25% of breakthrough cases had moderate or severe disease. Children who were vaccinated ≥ 5 years previously had a 3.7-fold higher risk of breakthrough disease than those who were vaccinated <5 years before. Vaccination at younger than 15 months of age was not significantly associated with an increased risk of breakthrough infection. CONCLUSIONS: Breakthrough varicella is not rare in Turkey where varicella infections are common. A longer interval since vaccination may be a risk factor for developing breakthrough varicella. Children who had been vaccinated >5 years previously were at risk for breakthrough disease. A two-dose varicella vaccine policy may be needed to provide improved protection.