The virus that causes shingles is cunning. It lies dormant inside the human body — often hiding in the nerve cells of the spinal column or the brain. Then, after decades of inactivity, it can remerge as a painful, blister-pocked skin rash.
“The way the virus is quiescent for decades and then reactivates — it’s unusual, but it makes sense from the perspective of the virus’ survival,” says Rafael Harpaz, MD, a medical epidemiologist with the CDC’s Division of Viral Diseases. Back when humans lived in small hunter-gatherer communities, Harpaz explains, viruses that depended on human hosts would have died out quickly if they infected everyone en masse. By lying in wait, shingles allows new generations of carriers to be born.
Harpaz has spent years studying the bug. A 2016 study of his in the journal Clinical Infectious Diseases helped shine a spotlight on a curious phenomenon: For at least the past 60 years, rates of shingles have been climbing. Compared to the period from 1945 to 1949, when 0.76 people per 1,000 developed shingles, rates climbed to 3.15 per 1,000 by the period from 2000 to 2007, his study found.
“[The rise] seems to be occurring across all age groups, and not just in the U.S.,” says Kosuke Kawai, ScD, an assistant professor of otolaryngology at Boston Children’s Hospital and one of Harpaz’s co-authors on the CID study. “There are studies in European countries, and also in Taiwan and Australia, that seem to show this same increase over time.”
While rates of shingles have been escalating for decades, Harpaz says the increase seems to be “plateauing” among older adults — a group that usually suffers from a higher incidence of shingles than younger people. (A new vaccine was introduced in 2006, and some experts suspect that may explain it.) But rates of shingles among those age 30 to 50 don’t seem to be leveling off.
From the late 1940s to the early 2000s, the prevalence of shingles among Americans younger than 50 more than quadrupled, Harpaz’s data shows. Some research suggests the incidence of shingles among younger adults may actually be gaining steam. At least anecdotally, shingles seems to be increasingly common among people in their twenties and thirties — a group that, historically, suffered from vanishingly low rates of the disease.
What’s fueling all this? Harpaz is stumped. “I have given this as much thought as anyone, and it remains a mystery to me,” he says.