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J Pediatr. 2001 Aug;139(2):297-304.

Childhood vaccination against varicella: persistence of antibody, duration of protection, and vaccine efficacy.

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Merck Research Laboratories, Merck & Co, Inc, West Point, Pennsylvania 19482, USA.



To document the duration of protection afforded by Oka/Merck varicella vaccine over a 7-year period.


The subjects were healthy children 1 to 12 years of age originally enrolled in clinical studies to evaluate the primary immune response to varicella vaccine 6 weeks after vaccination. Each was monitored for antibody persistence, breakthrough infection, and household exposure to varicella to produce estimates of vaccine efficacy.


The 6-year cumulative varicella antibody persistence rate was 99.5% (95% CI: 98.9%, 100.0%). The annual breakthrough rate through 7 years ranged from 0.2% to 2.3% per year; the estimated cumulative event rate was 6.5%. Comparison of the observed average annual breakthrough rate with the age-adjusted expected annual incidence rate of varicella in unvaccinated children corresponded to an estimated vaccine efficacy of 93.8% to 94.6%. Eighty vaccinated children were exposed to varicella in the household, resulting in 8 (10%) cases of infection. When compared with the historical attack rate of 86.8% in unvaccinated susceptible persons exposed to varicella in the household, this yields an estimated vaccine efficacy of 88.5% (95% CI: 80.9%, 96.1%). Varicella cases in vaccinated children generally were mild.


The live attenuated varicella vaccine is highly effective in inducing persistent immunity and long-term protection against breakthrough varicella infection.

[Indexed for MEDLINE]

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