Every year nearly 1 million new cases of shingles occur in the U.S., and one in three adults will contract the virus in their lifetime. Shingles is caused by varicella zoster virus, which also causes chicken pox. Despite those staggering numbers, two-thirds of adults will not contract shingles. Building on previous work that links childhood asthma to increased risk of shingles, researchers at the Mayo Clinic pursued a population-based study to understand the roots of this epidemic.

The study, published in the Journal of Allergy and Clinical Immunology, was conducted by Young Juhn, a professor of pediatrics and asthma epidemiologist at the Mayo Clinic’s Children’s Research Center, where he has been studying pediatric asthma for years. His team found that having asthma, regardless of age, increases the risk of contracting or reactivating the varicella zoster virus.

Since approximately 16 percent of the U.S. population has asthma, Juhn’s research provides a missing link in understanding the high prevalence of shingles cases. 

Juhn’s previous study, published in 2013, demonstrated an association of asthma with increased risk of respiratory infections such as acquired pneumonia or pertussis (whooping cough), and also common respiratory infections including strep throat and ear infections. “The results prompted us to look at whether this is true for non-respiratory conditions,” Juhn tells mental_floss

The earlier research showed that asthma patients suffer an impairment to innate immune function—the body’s first line of defense against infection or illness, in which the inflammatory response of the body is first activated. However, Juhn was interested in “whether this dysfunction could extend to adaptive immune dysfunction,” the body’s more evolved, antigen-specific immune response that sends lymphocytes out to fight infection. “To discern that, I needed to get out of the airways. We picked shingles because of its high morbidity rate,” he says. 

The researchers pulled medical records for patients who met “predetermined criteria for shingles” from residents of Olmstead County, Minnesota, which Juhn says “is a very special, isolated environment, where residents primarily receive medical care from two main medical centers.” Through the Rochester Epidemiology Project database that links patient information between the two medical centers, they pulled 371 cases of patients with shingles—with an average age of 67—and compared them against 742 control subjects. They did a similar review to pull asthma cases. They found that 23 percent of these shingles patients also had asthma, compared with only 15 percent from the control group. Adults with asthma had an approximately 70 percent higher risk of developing shingles than those without asthma.

They also confirmed that non-asthmatic allergic disorders like atopic dermatitis (eczema) were associated with an increased risk of shingles. “This is consistent with biologic coherence,” Juhn says. “We found that there is some trend toward increased risk of shingles with allergic rhinitis and food allergies, too.” Their work casts new light on the existing body of literature that suggested shingles is a result of the immune system becoming weaker over time with aging. “Our study says that the association is not limited to people older than age 60,” says Juhn. “The study finds an association between asthma and risk of shingles across the board, with no age-specific factor.”

While the mechanisms of the increased risk are still not fully understood, Juhn says they believe that asthma suppresses adaptive immune function, which may increase the risk of varicella zoster virus reactivation. 

Furthermore, the study was able to clear up two “controversies,” that formerly linked corticosteroids, and the zoster vaccine itself to an increased risk of shingles, which they did not find. “I want to make clear that clinicians and patients with asthma should not be overly concerned about the effects of inhaled or systemic corticosteroids, so they should receive proper asthma treatment to achieve asthma controls,” says Juhn. “Also, vaccinations are important given the significant morbidity involved with shingles. Children and adults should receive age-appropriate zoster vaccinations.”

The next step in their research will be to study the mechanism of asthma to impact the adaptive immunity, and will extend their study to look at other vaccine-preventable diseases such as whooping cough.