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Exposure to chickenpox as adult does not fully protect against shingles

Adults re-exposed to the herpes zoster virus found to be around 30% less likely to develop shingles

Ingrid Torjesen

Thursday, 23 January 2020

Adults exposed to a child with chickenpox (varicella) in the home are less likely to develop shingles but are not fully protected, suggest the results of a study* published in The BMJ.

The results support the theory that re-exposure to the herpes zoster virus in adulthood (after chickenpox infection as a child), boosts immunity to shingles.

Primary infection with varicella zoster virus causes chickenpox, typically in children. After this initial infection, the virus remains in the body as a dormant infection, and reactivation, often decades later, causes shingles. There is a theory that re-exposure to the varicella zoster virus in adulthood boosts immunity to shingles (exogenous boosting) so the UK and many other countries do not offer routine childhood varicella vaccination as this would remove circulating virus in the community.

However, this latest study found that adults re-exposed to the virus were around 30% less likely to develop shingles over 20 years rather than completely protected, prompting the researchers to call for a review of the UK's childhood varicella vaccination policy, which assumes re-exposure in adulthood confers complete immunity to shingles for between two and 20 years.

In order to estimate the risk of herpes zoster after exposure to a household member with varicella, the researchers accessed UK general practice and hospital records for 9,604 adults diagnosed with herpes zoster between 1997 and 2018 who lived with a child (18 or under) with varicella during an average 15-year observation period.

Average age at zoster diagnosis was 41 years and at first known exposure to varicella was 38 years. After adjusting for age, calendar time, and season, strong evidence suggested that in the two years after household exposure to a child with varicella, adults were 33% less likely to develop zoster compared with baseline (unexposed) time. In the 10 to 20 years after exposure, this protective effect waned slightly but adults were still 27% less likely to develop zoster compared with baseline time. A stronger boosting effect was seen among men than among women after exposure to varicella.

The authors said: "These findings cannot be used to justify for or against specific vaccination schedules. They do, however, suggest that previous mathematical models, estimating the effect of exogenous boosting in childhood varicella vaccination policy in the UK, that assume complete immunity for between two and 20 years may need revisiting."


*Forbes H, Douglas I, Finn A, et al. Risk of herpes zoster after exposure to varicella to explore the exogenous boosting hypothesis: self controlled case series study using UK electronic healthcare data BMJ 2020; 368 :l6987

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