Associate Professor Jonathan R. Carapetis, one of the authors of the article, comments:
There is no definitive answer to this very pertinent question. The main problem lies in deciding whether the rash is vaccine-associated or a potential infection with wild varicella zoster virus that happens to have occurred in the period following immunisation. If it is vaccine-associated, the risk of transmission is incredibly low. I consulted the world's leading expert on the vaccine, Professor Anne Gershon of Columbia University in New York, who informed me that so far out of over 40 million doses of vaccine distributed, there are only four instances of transmission and all contact cases were mild. Therefore, there is no need to give varicella zoster immunoglobulin to any contact of a definitely vaccine-associated rash, whether pregnant, immunocompromised or otherwise. If a clinical illness consistent with varicella subsequently occurred in a pregnant or immunocompromised contact, it would be sensible to treat early with aciclovir.
How to decide if the rash is vaccine-associated? Most vaccine-associated rashes occur several weeks after immunisation (median about three weeks), consist of just a couple of papules or vesicles, and are not associated with systemic symptoms. If there are more than just a few lesions, or there are systemic symptoms, and especially if the rash occurs in the first week or two following immunisation, then it is more likely to be due to infection with a wild virus. If you are really uncertain, then err on the side of assuming a wild infection, and give zoster immunoglobulin to high-risk contacts, provided the exposure fits within the guidelines recommended in the Immunisation Handbook.1
