To the Editor.—

The statement by Johnson et al1 that varicella was "protective against 96% of exposures" is misleading. Protection implies that disease was prevented. A continuing household exposure, eg, to a sibling, would be expected to produce an attack rate approaching 100%.2 Only four vaccinees had this type of exposure; 49 had other less intense types of exposure. The outcomes of other types of exposure are far less predictable but normally are not nearly as likely to result in varicella.3

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