(HealthDay News) – Varicella vaccination is effective for preventing varicella, with effectiveness lasting over a 14-year period, according to a study published online April 1 in Pediatrics.

Roger Baxter, MD, of the Kaiser Permanente Vaccine Study Center in Oakland, Calif., and colleagues followed a cohort of 7,585 children vaccinated with varicella vaccine in their second year of life (1995) through 2009 for breakthrough varicella and herpes zoster. Of the children, 2,826 received a second dose in 2006–2009.

The researchers found that the average incidence of varicella was 15.9 per 1,000 person-years among the vaccinated children, which was nine- to 10-fold lower than in the pre-vaccine era. At the end of the study period, vaccine effectiveness was 90%, with no evidence of waning over time. The majority of cases of varicella occurred soon after vaccination, and most cases were mild. None of the children who received a second dose developed varicella. The rate of herpes zoster was lower for vaccinated children than unvaccinated children in the pre-vaccine era (relative risk, 0.61), and cases of herpes zoster were mild.

“This study confirmed that varicella vaccine is effective at preventing chicken pox, with no waning noted over a 14-year period,” the authors write.

Several authors disclosed financial ties to the pharmaceutical industry.

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