Since 2017, experts have urged adults ages 50 and up to get the two-dose Shingrix vaccine against shingles. Now a new study published in the Annals of Internal Medicine in January confirms that yes, the vaccine is providing lasting protection to people in the “real world.”

Shingles is a viral infection that causes a blistering rash, sometimes accompanied by a fever, headache, or fatigue. Most notoriously, it can be intensely painful, with symptoms lasting several weeks. Some people develop post-herpetic neuralgia—nerve pain that persists for months or even years after the shingles rash clears up. According to the CDC, over one million Americans are diagnosed with shingles each year, and one in three will develop it in their lifetime.

The culprit behind shingles is the varicella-zoster virus, the same one that causes chickenpox. Once you’ve had chickenpox, the virus remains in your body, dwelling inactively in nerve tissue. That is, unless the virus is reactivated—possibly due, for instance, to lowered immune system defenses but usually for no known reason.

That’s where shingles vaccination comes in. Back in 2017, the FDA approved the Shingrix vaccine after clinical trials showed that it was at least 90 percent effective over four years in preventing shingles among older adults. The vaccine—given in two doses, two to six months apart—replaced an older, less effective shingles vaccine.

Currently, the CDC recommends Shingrix for preventing shingles in people 50 and older. Younger adults who have a compromised immune system due to an underlying medical condition should also get vaccinated. The question has been whether the high success levels seen in clinical trials would translate to the real world. The new findings suggest that the answer is largely yes.

For the study, researchers tracked medical records from nearly two million Americans ages 50 and older who were enrolled in any of four large health systems from 2018 through 2022. During that time, 38 percent received at least one Shingrix dose, while 29 percent received both doses.

Over four years, the study found, the two-dose vaccine was 76 percent effective, overall, in preventing shingles. To put it in more concrete numbers, people who remained unvaccinated developed shingles at a rate of just under seven cases per 1,000 each year; among fully vaccinated people, there were just under two cases per 1,000 each year.

That effectiveness figure is lower than seen in clinical trials but still shows that the vaccine offers a strong buffer against shingles. Importantly, the protection held up, waning only a little over four years. On average, the two-dose regimen was 79 percent effective in the first year, and 73 percent effective in years three and four.

A critical point here: This means the two-dose vaccine is effective for at least four years. Follow-up studies from the aforementioned clinical trials showed that the protection was maintained for at least seven years. And it likely lasts far longer than that, according to John Swartzberg, MD, an infectious disease specialist and chairperson of the Wellness Letter editorial board. That’s why the CDC does not recommend a Shingrix booster at this point.

You do, however, need that second dose. In the Annals study, those who received only one dose of Shingrix did get some shingles protection, versus unvaccinated people—but it faded fairly quickly. Over year one, that single dose was 70 percent effective, before dropping to 45 percent in the second year.

It’s best to get that second dose within the recommended six-month window. But the good news is, if you can’t get it then, all is not lost. For people in this study, the second dose boosted the vaccine’s effectiveness against shingles, even if it was delayed beyond six months.