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Although varicella vaccine was licensed in 1995, questions remain about long-term efficacy against chicken pox and its effect on the incidence of shingles (herpes zoster). Investigators at Kaiser Permanente (some with financial ties to the vaccine manufacturer) followed 7585 children aged 12 to 23 months after they received their first varicella vaccine between June and November 1995 through 2009 (retention rate, 97%).
Of 1505 reported breakthrough varicella cases (>6 weeks after vaccination), 74% were mild (≤50 lesions) and no cases were reported in patients who had received two doses of vaccine. This rate was 9 to 10 times lower than the prevaccine rate, with an overall vaccine effectiveness of 90%. A total of 46 confirmed cases of herpes …