CONTEXT: This study will assess the incidence of herpes zoster over time among patients who receive the varicella vaccine. Through natural exposure to the wild-type varicella virus the human body's cellular immunity is boosted, which in turn wards off herpes zoster by inhibiting reactivation of the varicella zoster virus. As universal vaccination for varicella occurs, and the effect of herd immunity is accomplished, it is hypothesized that the resulting decrease in the naturally circulating wild-type varicella virus in the environment will result in an increase in the overall incidence of herpes zoster among immunized individuals over time.
STUDY DESIGN: A retrospective study with data analyzed through the Centers for Disease Control and Prevention's Vaccine Adverse Event Reporting System from the years 2002 to 2004. The subject population analyzed includes all patients who received the varicella vaccine, which include 2,663 from 2002, 1,940 from 2003, and 421 from 2004, for a total of 5,024 subjects .. A subset of 154 subjects were analyzed who received the varicella vaccine and reported herpes zoster during the time frame assessed and include 120 from 2002, 27from 2003, and 7 from 2004.
RESULTS: An incidence rate of herpes zoster was calculated to be 3 % of overall adverse events reported for varicella vaccine recipients. Eighty percent of the subjects in this population were less than 13 years of age. It was found that the majority of the herpes zoster outbreaks occurred within the first year after receiving the varicella vaccine, with most of these occurring by approximately day 7 following immunization. The incidence in both males and females was similar with a 14% difference in males greater than females.
CONCLUSIONS: This study reveals that herpes zoster occurs as 3% of the adverse events c reported to VAERS regarding the varicella vaccine. When the varicella vaccine was implemented there were initial hopes that vaccine recipients would not experience herpes zoster after vaccination or minimally a decreased occurrence of outbreaks of herpes zoster as a benefit. This study indicates that herpes zoster does occur in the population immunized with the varicella vaccine. Further, long term studies need to be conducted following a control group of the normal population, who acquire the varicella virus naturally, as well as varicella vaccine recipients, in order to assess the long term incidence rate of herpes zoster in individuals with the wild-type varicella virus and those with the Oka attenuated varicella strain.
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