Chickenpox vaccine and shingles: cases are falling in young adults and rising from age 35

The first Americans vaccinated against chickenpox as children are now in their early thirties, and they are getting shingles less often than the generation before them did at the same age. That is the main result of an analysis released on October 2 by Epic Research, which studies health trends in electronic medical records. Epic researchers used electronic health data from more than 85 million patients seen by healthcare providers in the United States.

The same data contain a second trend that runs the other way. Among people aged 35 and over, most of whom caught chickenpox as children, shingles is becoming more common.

Both trends turn on how the two diseases are related.

How chickenpox and shingles are linked

Chickenpox and shingles are two stages of one infection. The cause is the varicella zoster virus. A first infection, usually in childhood, produces chickenpox, known medically as varicella. When the rash clears the virus does not leave. It settles in nerve cells and stays dormant, sometimes for the rest of a person’s life.

Shingles, called herpes zoster by doctors, is what happens when the dormant virus reactivates. It produces a painful, blistering rash that usually appears on one side of the body. Reactivation becomes more likely as the immune system ages.

The burden is substantial. A review of 130 studies from 26 countries found that the incidence rate ranged between 3 and 5/1000 person-years in North America, Europe and Asia-Pacific. In a group of 1,000 people followed for a year, three to five developed shingles. That review was written by employees of Merck, a vaccine maker.

The rash heals, and the pain sometimes does not. The most common complication is severe long-term nerve pain, a condition called postherpetic neuralgia. The global review found that the risk of developing it varied from 5% to more than 30% of shingles patients, depending on age and how it was defined.

The link between the diseases is the reason a chickenpox vaccine might prevent shingles. The vaccine contains a weakened form of the virus. A person who never has the natural infection carries no full-strength virus to reactivate later.

What the new data show on shingles in young adults

The Food and Drug Administration approved the first chickenpox vaccine in 1995. Children immunized as toddlers that year are now about 32.

Epic’s analysts counted shingles diagnoses in each age group every year from 2019 to 2026, NBC News reported.

Age group	Women, cases per 10,000, 2019 to 2026	Men, cases per 10,000, 2019 to 2026
18 to 24	2.9 to 1.6	2.7 to 2.4
25 to 29	7.7 to 3.2	7.5 to 3.0
30 to 34	10.8 to 7.3	11 to 7.3

Among 25- to 29-year-olds, rates of shingles cases more than halved. Shingles cases dropped from 10.8 to 7.3 per 10,000 people for women ages 30 to 34 between 2019 and 2026, with a similar fall in men.

“Our data suggest that trend is now reversing in the very youngest adults, the first generation eligible to be vaccinated against chickenpox as children,” said Kersten Bartelt, a registered nurse and lead author of the report. The trend being reversed is a decades-long rise in shingles.

Bartelt added a caution that applies to everything that follows. Because shingles is typically rare in people younger than 50, the data can’t prove whether the protection will last as they age.

What earlier studies found on the chickenpox vaccine and shingles

The Epic result extends a pattern first seen in children.

The largest pediatric study pooled records from six US health systems covering 6.4 million children between 2003 and 2014. The shingles rate among vaccinated children was 38 per 100,000 person-years, which was 78% lower than that among children who were unvaccinated. Overall, pediatric shingles declined by 72% over the 12 years.

That study also shows the vaccine’s limit. Vaccinated children did get shingles. They got it far less often.

Researchers at the Centers for Disease Control and Prevention tracked the national picture in insurance claims. In children, they reported, the incidence has declined in a step-wise pattern since the varicella vaccination program’s introduction.

The fullest version of that analysis was published in 2022. The CDC team began from an admission: when the US varicella vaccination program was introduced in 1995, its impacts on the epidemiology of herpes zoster (HZ) were not precisely known. Epidemiology means the pattern of who gets a disease, and how often. They used claims from 1998 to 2019 to compare people born before 1990 with those born after.

Among people under 30, shingles rose at first in the oldest age bands, whose members had been born before the vaccine arrived. It later declined in a stepwise pattern once each age group was comprised of persons born in the postvaccine period. As each vaccinated birth year aged into a new bracket, that bracket’s rate dropped.

The authors predicted what Epic has now reported. They wrote that continued declines in age-specific HZ incidence as varicella-vaccinated cohorts age are likely.

The unexplained rise in shingles from age 35

The Epic data also showed that rates of shingles are rising among people 35 and over. There is no clear evidence for what is causing the rise in this group, NBC reported.

One long-standing explanation involves chickenpox itself. Adults who had chickenpox as children were, for most of history, regularly re-exposed to the virus by children around them, and each exposure may have topped up their immunity. Scientists call this exogenous boosting, meaning a boost from outside. “Before the vaccine was available, parents in their 20s, 30s, 40s, and grandparents, were exposed to younger children with chickenpox, so that was like a booster for them,” Sharon Curhan, a physician and epidemiologist at Brigham and Women’s Hospital, told NBC. Curhan was not involved in the analysis.

If boosting matters, removing chickenpox from circulation could raise shingles rates in adults for a generation. Mathematical models predicted that before vaccination programs began.

The best direct test comes from Britain, which did not vaccinate children against chickenpox during the study period. Researchers at the London School of Hygiene and Tropical Medicine identified 9,604 adults with shingles who had lived with a child who caught chickenpox. In the two years after household exposure to a child with varicella, adults were 33% less likely to develop zoster than at other times. In the 10-20 years after exposure, adults were 27% less likely to develop herpes zoster.

So the boosting effect, if real, appears to be modest. The authors’ reading was that exogenous boosting provides some protection from the risk of herpes zoster, but not complete immunity, which is less than earlier models had assumed.

Other evidence suggests the loss of boosting is not the main driver. The rise in adult shingles is older than the vaccine. The global review found that a temporal increase in the incidence of HZ was reported in the past several decades across seven countries, often occurring before the introduction of varicella vaccination.

The CDC’s American data point the same way. In adults born before 1990 the team saw age-specific increases in HZ incidence during the earlier study years, with decelerations in later years, starting with the oldest groups. A vaccine-driven surge would be expected to accelerate as chickenpox disappeared. The authors concluded that their results do not support prior modeling predictions that the varicella vaccination program would increase HZ incidence among adult cohorts who previously experienced varicella.

What does explain the long rise is unknown. An earlier CDC analysis of adult trends described ongoing increases among younger adults but deceleration in older adults, and ended with a plain statement: “The patterns are not readily explained.” Curhan mentioned stress, depression and autoimmune conditions as candidates, without evidence establishing any of them.

How shingles is prevented in older adults

For people who have already had chickenpox, the childhood vaccine comes too late. A separate vaccine against shingles exists for them.

Its main trial enrolled 15,411 adults aged 50 or older in 18 countries, who received two injections of vaccine or placebo two months apart. During a mean follow-up of 3.2 years, herpes zoster was confirmed in 6 participants in the vaccine group and in 210 participants in the placebo group. Overall vaccine efficacy against herpes zoster was 97.2%, with a plausible range from 93.7% to 99.0%.

Side effects were common. Symptoms in the more severe category, grade 3, were reported by 17.0% of vaccine recipients and 3.2% of placebo recipients. Serious adverse events occurred at similar rates in both groups. The trial was funded by the vaccine’s manufacturer.

In the United States the CDC currently recommends two doses of the varicella vaccine for children from ages 1 to 6. Who is offered a shingles vaccine, and at what age, varies between countries and depends on age and immune status, which is assessed by a person’s doctor.

What is not yet known about the chickenpox vaccine and shingles

The Epic analysis is a company report. It counts shingles diagnoses by age group in electronic health records, and trends by age group cannot show what happened to vaccinated individuals as against unvaccinated ones. It shows that shingles fell in age groups where most people were vaccinated. The pediatric study, which did compare individuals, supports the same conclusion in children.

Trends in diagnosis can shift for reasons unrelated to disease. Changes in how often people see a doctor, or in how shingles is coded, alter the counts. The CDC team checked for this by looking at shingles as a share of all emergency visits and found similar patterns.

Observational data cannot settle the adult question. The British household study found an association consistent with boosting, but it studied people who had shingles and cannot say how much adult rates changed in countries that vaccinate.

The largest uncertainty is time. Shingles is mainly a disease of people over 50, and the oldest members of the vaccinated generation are in their early thirties.

Shingles is falling in the first generation vaccinated against chickenpox, and that generation is still too young for anyone to know whether the protection holds at the ages when shingles is most common.