An experimental vaccine for shingles—a painful nerve and skin infection—cut the number of shingles cases in half in one of the largest clinical trials of an adult vaccine ever. The vaccine also dramatically reduced the severity and complications in people who got the disease.

Shingles, also known as herpes zoster, is caused by the same virus that causes chickenpox. Once chickenpox infection runs its course, some of the virus lingers in sensory nerve cells, usually near the spinal cord, where the virus stays dormant for years. As immunity weakens with advancing age, the virus can reactivate, multiply and damage the nerve cells to cause pain. It then migrates to the skin, where it causes pain, itching or tingling before turning into a painful blistering rash that can take two to four weeks to heal. A serious complication of shingles is postherpetic neuralgia (PHN)—a form of chronic nerve pain that lasts for 3 months or longer. Nearly one-third of older people with shingles experience PHN.

The study, which was led by the Department of Veterans Affairs and carried out in collaboration with NIH’s National Institute of Allergy and Infectious Diseases and Merck & Co., Inc., involved more than 38,500 men and women age 60 or older. The vaccine used in the study is a new, more potent version of the vaccine that has been used to prevent chickenpox in children since 1995. Half of the participants received a single injection of the vaccine (a live, weakened form of the virus) and the other received a placebo vaccine.

During an average of more than three years of follow-up, the vaccine reduced the incidence of shingles by 51 percent; 642 cases of shingles occurred among those in the placebo group compared with only 315 in the vaccinated group. In addition, the pain and discomfort in those who got shingles was 61 percent lower in those who had gotten the vaccine. The vaccine also reduced the incidence of PHN by two-thirds compared with placebo.

This is the first time that a vaccine has proven effective against shingles. Merck has already submitted a license application to the Food and Drug Administration for the vaccine. The research team estimates the vaccine could potentially prevent 250,000 cases of shingles in the U.S. each year and significantly reduce the severity in another 250,000.