Jan. 22 (UPI) -- Adults exposed to a child with chickenpox in the home are less likely to develop shingles, but vaccination still offers the best protection even if it doesn't provide the long-standing immunity previously thought, a new analysis has revealed.
In an article published Wednesday in BMJ, researchers in England note that their findings support the theory that re-exposure to the herpes zoster virus as an adult, after having chickenpox as a child, boosts immunity to the disease but does not provide complete protection.
Infection with varicella zoster virus causes chickenpox. After this initial infection, the virus remains dormant in the body, and reactivation, sometimes years later, causes shingles.The theory that re-exposure to the varicella zoster virus in adulthood boosts immunity to shingles -- a process called exogenous boosting -- has gained widespread support.
However, the latest findings suggest that this boosting may not last as long as previously thought -- an important consideration given that many countries, including England, don't recommend routine vaccination against the virus.
For their research, the authors reviewed general practice and hospital records for 9,604 adults diagnosed with herpes zoster between 1997 and 2018 who lived with a child 18 years of age or younger with varicella during an average 15-year observation period.
After adjusting for age, calendar time and season, they found that in the two years after household exposure to a child with varicella, adults were 33 percent less likely to develop shingles.
However, 10 to 20 years after exposure, adults were only 27 percent less likely to develop the disease, suggesting that immunity may have a window. And in general, a stronger boosting effect was seen among men than among women after exposure to varicella.
Currently, the U.S. Centers for Disease Control and Prevention recommends the varicella vaccine for all children, and it's been estimated that as many as 90 percent of American children receive the shot.
The agency notes that, while how long a vaccinated person is protected against varicella remains unknown, live vaccines typically produce antibodies against the virus for at least 10 to 20 years afterward, according to the agency.
"(Our) findings cannot be used to justify for or against specific vaccination schedules," the authors wrote. "They do, however, suggest that previous mathematical models, estimating the effect of exogenous boosting in childhood varicella vaccination policy in the U.K., that assume complete immunity for between two and 20 years may need revisiting."