Children who are vaccinated against the virus that causes chickenpox are getting a twofer: Not only are they protected against irritating and potentially scarring chickenpox, but they appear to have a “dramatically” lower risk of developing shingles in childhood than unvaccinated kids who contract the disease, according to a large, new multiyear study.
The rate of shingles cases in vaccinated children was 78% lower than it was among unvaccinated children who had contracted the virus, varicella, the authors reported Monday in the journal Pediatrics.
Overall over the 12-year period studied, the rate of shingles cases among all children in the study fell by 72%, as increasing numbers of vaccinated children likely led to a decrease in infections among unvaccinated children through a phenomenon called herd immunity.
As the amount of immunity against a pathogen like the varicella virus grows in a given population, it becomes harder for the virus to find and infect children who aren’t vaccinated.
“So the vaccine is not only preventing chickenpox, but there’s an added benefit thrown in that we had hoped would happen,” said Dr. Anne Gershon, a pediatric infectious diseases professor at Columbia University, said of the finding of reductions in shingles cases among children.
Gershon was not involved in the research, but she wrote a commentary on it that the journal published in conjunction with the study. “That the varicella vaccine prevents not only varicella but zoster as well is an exciting dual benefit from the varicella vaccine, further improving the health of children by immunization,” she wrote. Herpes zoster is the proper name for shingles.
The study, which was funded by the Centers for Disease Control and Prevention, mined the medical records of more than 6 million children to try to tease out an answer of whether the varicella vaccine would protect against shingles, or potentially increase the risk of developing the painful condition.
Shingles is a delayed complication of varicella infection. The virus hides in the body of people who have had chickenpox. Normally the immune system keeps it in check. But the virus can reactivate, causing painful rashes that can lead to long-term nerve pain. It is estimated that about one-third of people who had chickenpox will go on to have at least one bout of shingles.
While the condition is more common in older adults whose immune systems are waning, children too can develop shingles.
The varicella vaccine is made with a live but weakened varicella virus, which can also lie dormant and later reactivate to cause shingles.
In 2013, the authors of the current study published an earlier investigation of shingles rates among vaccinated children. They found a substantially lower rate among vaccinated children overall, but a significantly higher rate among children between the ages of 1 (around the time the first dose of two doses of vaccine is given) and 2.
They set out to dig further into that finding. Lead author Sheila Weinmann, senior investigator with Kaiser Permanente Northwest Center for Health Research, said they felt it was important to find out what was going on.
The first study followed 322 children for four years. For the second study, the group looked at medical records of nearly 6.4 million children under the age of 18, calculating rates of shingles over 12 years.
They did see a higher rate of shingles among vaccinated 1-year olds as compared to unvaccinated children. But that difference quickly reversed. Among 2- and 3-year olds, there wasn’t really a marked difference between the vaccinated and unvaccinated children. By age 4, the rates of shingles among unvaccinated children started to climb; among vaccinated children, it declined slightly and then remained at a low and relatively stable rate.
The reason for the earlier shingles rate among 1-year-olds? They were being exposed to varicella virus before the unvaccinated children were. “If they hadn’t ever had chickenpox then they weren’t going to be likely to get shingles,” Weinmann said of the unvaccinated 1-year olds.
But given the highly infectious nature of the varicella virus, that quickly changed, as the rates among older unvaccinated children showed. In the era before the varicella vaccine came on the market, virtually everyone contracted chickenpox in childhood; the CDC estimated that every year about 4 million children were infected.
So among older unvaccinated children, shingles rates rose after chickenpox infections. Overall there were 38 cases of shingles per 100,000 person years in the vaccinated group, compared to 170 cases per 100,000 person years among the unvaccinated children.
Whether the vaccinated children will continue to have lower rates of shingles as they move into the later stages of life remains to be seen, Gershon said, as does whether those vaccinated in childhood will need a varicella booster vaccine at some point in adulthood.