December 12, 2002
An Outbreak of Varicella among Vaccinated Children
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At a day-care center in New Hampshire, an outbreak of varicella affected 25 healthy young children, including 17 who had been vaccinated against varicella. The index patient was a four-year-old who had been vaccinated three years earlier. In this outbreak, the effectiveness of previous varicella vaccination was only 44 percent against disease of any severity, but it was 86 percent against moderate or severe disease.
This outbreak in a population with good vaccination coverage shows that varicella can be highly infectious among vaccinated, healthy children. The effectiveness of the vaccine was well below the estimates of 71 to 100 percent from earlier investigations.
