Anyone who has contracted the shingles virus knows how excruciatingly painful it can be: About 1 out of every 3 people in the United States will develop shingles, also known as herpes zoster, in their lifetime, according to the U.S. Centers for Disease Control and Prevention.

At greatest risk are the 99% of Americans born in or before 1980 who had chickenpox and have not been vaccinated against shingles. And while the shingles vaccine is highly effective, protection can wane over time.

To learn more about the virus, we talked to two experts: Dr. Kieron S. Leslie, professor of clinical dermatology at UCSF School of Medicine, and Dr. Jennifer Yeh, clinical assistant professor of dermatology at Stanford University School of Medicine.

Question: What is shingles?

Leslie: It’s an infection caused by varicella zoster virus, the same virus as chickenpox. When people get chickenpox as children, the virus can hide away in the nervous system. And at a later point in their lives, it can be reactivated, following the distribution of nerves in the skin.

Q: What are the symptoms?

Yeh: Typically, there is a “pre-eruptive” phase, in which a patient has pain and burning in a particular area of the body. And then, a few days later, they may develop a rash there, with some red bumps as well as some blisters.

Q: Who is vulnerable?

Leslie: We most commonly see shingles in people who are over age 60. And those who are immunosuppressed.

Q: Is it dangerous?

Leslie: Most of the time, shingles causes a painful rash that heals in one to two weeks. But some folks, especially older people, can be left with nerve pain after the rash heals. That can last for many months.

Q: Is there treatment?

Yeh: Typically we treat it with antiviral medicines. It is recommended to start within the first 72 hours of the symptoms in order to really shorten the severity of that episode. We use valacyclovir (Valtrex) or acyclovir (Zovirax). A drug called foscarnet (Foscavir) is reserved for cases that are resistant to the first two antivirals.

Q: Why would someone be hospitalized?

Leslie: Shingles rarely causes serious illness. But it can be widespread over the body. If it affects the eyes, it can cause blindness. It can go to the brain and cause some inflammation there. It can cause pneumonia. So a small proportion of people would be admitted to the hospital with problems, because there are potentially serious outcomes.

Q: Is it contagious?

Leslie: You get shingles from yourself — it’s reactivated in your nerves. If you’ve already had chickenpox or the chickenpox vaccine, you’re not at risk of getting shingles from someone else. But if you’ve never had chickenpox or the vaccine, and you come in contact with somebody with shingles, you may get chickenpox. It’s highly infectious.

Q: Is there a vaccine?

Yeh: Absolutely. It’s a two-dose vaccine, with each dose separated by two to six months, called Shingrix. It’s recommended for adults ages 50 or older, and also for adults 19 years or older who have a weakened immune system.

It provides strong protection against shingles. It also helps protect against one of the complications that is common after shingles, called “post herpetic neuralgia,” which is the lingering pain and burning even after the case of shingles has resolved.

It’s highly recommended to get the vaccine, even if you’ve had shingles in the past or if you’ve had the chickenpox vaccine, as well.

Q: How effective is the vaccine?

Leslie: No vaccine is 100% effective. In adults over the age of 70, Shingrix is 89% effective. We consider that a really good vaccine.

Yeh: Protection may wane over time. That would mean a discussion with your primary care doctor as to whether you need another dose.

Q: Are there side effects from the vaccine?

Leslie: There’s a sharp pain when you get the injection. And you may feel a sore arm for a few days, potentially with redness where you got the shot. Sometimes people feel a little bit tired, with muscle pain and a headache, for a few days after the injection.

Q: Is there the risk of getting shingles from the vaccine?

Yeh: You will not get shingles from the vaccine. That’s because the vaccine contains only a small portion of the varicella zoster virus.

Q: Is the vaccine covered by insurance?

Yeh: Definitely. But oftentimes it’s limited to people who are age 50 and older, because that is what the CDC’s Advisory Committee on Immunization Practices recommended.

It is covered by Medicare’s prescription drug plan, called Part D. And most private insurance plans will cover the vaccine, if you’re over age 50. Older adults with Medicaid benefits also will receive the vaccine.