By Pat Anson, Editor

Vaccinating young children against chicken pox nearly doubles the incidence of shingles in the wider population, according to a new study in Belgium. However, researchers concluded that the risk of shingles is outweighed by the benefits of vaccination.

Several countries, including the United States, Australia, Japan and Germany, have virtually eliminated childhood cases of chickenpox by requiring children to be vaccinated against the chickenpox (varicella-zoster) virus.

But health officials in other countries have hesitated to launch vaccination programs because they believe that exposure to people with chickenpox naturally boosts the immunity of people who have already been infected.

Re-exposure to the virus was thought to have protective benefits for as long as 20 years. However, in the study published in the journal eLife, scientists from the Universities of Antwerp and Hasselt (Belgium) used computer models to estimate that the extra protection only lasts for about two years.   

"Our findings should allay some fears about implementing childhood chickenpox vaccination," said lead author Dr. Benson Ogunjimi.

"We were surprised to find that re-exposure to chickenpox is beneficial for so few years and also that the most pronounced effect of vaccination on increasing cases of shingles is in younger adults.”

The chicken pox virus persists in small numbers in nerve cells for many years after an infection, and can reactivate from these cells. Often this reactivation causes no symptoms, but sometimes it results in shingles, a painful rash that can lead to a chronic pain condition called postherpetic neuralgia that is difficult to treat.

Researchers found that the increase in shingles is likely to occur among 31- to 40-year-olds. Previous models predicted that older age groups would bear the brunt of a rise in shingles. Younger adults are less likely to develop lasting complications from shingles.

Together, researchers say their findings should allay some fears about implementing chickenpox vaccination programs, because the benefits of re-exposure are limited and younger adults are more likely to be impacted.

Shingles occurs most often in individuals with a weakened immune system, such as HIV or cancer patients. Older adults may also be more susceptible to shingles after a Cytomegalovirus infection, another virus in the herpes family.