What Are the Side Effects of the Mpox Vaccine? Doctors Explain

What Are the Side Effects of the Mpox Vaccine? Doctors Explain

There are a lot of questions about mpox (previously known as monkeypox) after the Centers for Disease Control and Prevention issued a recent warning that “the outbreak is not over.”

As you might remember, mpox dominated headlines last summer as the virus quickly spread across the U.S. and other countries. While public health officials were able to get cases under control within a matter of months, mpox is still out there. And, in fact, the CDC warns that there could be a “resurgence” in cases this summer.

More than 30,400 cases of mpox have been reported in the U.S. since May 10, and, at the height of the outbreak, there were 460 new cases per day, according to CDC data. With that, the CDC is advising people who are considered high risk for mpox (more on that in a moment) to get vaccinated against the virus.

Of course, it’s understandable to have questions about the vaccine, including its side effects. Here’s what you need to know.

What is the mpox (monkeypox) vaccine?

There are actually two monkeypox vaccines licensed for use in the U.S.—ACAM200 and JYNNEOS (which also go under the names Imvamune or Imvanex). They’re licensed to prevent smallpox but also work to prevent monkeypox, per the CDC.

ACAM2000 is given as a live virus preparation that’s given by pricking the skin surface, the CDC explains. A lesion—called a “take”—will develop at the site of the vaccination, but the virus that grows at the site of the lesion can be spread to other parts of the body or even to other people. Because of this, people who are vaccinated with ACAM2000 have to take special precautions to avoid spreading the virus. People who get the vaccine are considered fully vaccinated after 28 days.

JYNNEOS is also a live virus vaccine but it’s non-replicating—meaning, it can’t spread or make you sick. It’s given as two injections four weeks apart and there’s no visible “take,” the CDC says. People who get the JYNNEOS vaccine are not considered vaccinated until two weeks after they get the second dose of the vaccine, the CDC says.

JYNNEOS is the preferred vaccine that’s used in the U.S., says Thomas Russo, M.D., professor and chief of infectious disease at the University at Buffalo. “It’s considered an improvement on ACAM2000 because it doesn’t replicate,” he says. It can also be given to people who are immunocompromised and have eczema, he points out— ACAM2000 can’t.

What are the monkeypox vaccine side effects?

It depends on which monkeypox vaccine you get. In general, the CDC says that the following can be side effects of the JYNNEOS vaccine:

The following may be side effects of the ACAM2000 vaccine, per the CDC:

  • Pain at the injection site

  • Swelling at the injection site

  • Redness at the injection site

  • Fever

  • Rash

  • Lymph node swelling

  • Complications from accidentally inoculating yourself

JYNNEOS “was designed to be less reactogenic than traditional smallpox vaccines and is comparable to routine vaccines in terms of injection site reactions,” says Amesh A. Adalja, M.D., a senior scholar at the Johns Hopkins Center for Health Security. William Schaffner, M.D., an infectious disease specialist and professor at the Vanderbilt University School of Medicine, agrees, noting that people tend to do “very well” with the JYNNEOS vaccine.

How long do mpox vaccine side effects last?

Again, Dr. Russo stresses that you’re unlikely to have many issues with the vaccine, if you have any side effects at all. “It’s usually maybe 24 hours or so, and often only local stuff,” he says. “I vaccinated a few people in a research lab. They had a little redness and swelling, but that was about it.”

The CDC notes that some people have reported experiencing thickening of the skin and skin discoloration in the spot where they’ve gotten the vaccine. These symptoms can last for several weeks, per the CDC.

How to treat mpox side effects

If you have side effects from the vaccine and it bothers you, Dr. Russo recommends taking a dose of acetaminophen (aka Tylenol). That’s true whether you have arm pain or flu-like effects. “I wouldn’t do much more than that,” he says.

When to see a doctor for mpox vaccine side effects

The mpox vaccine is generally considered a safe vaccine, and there are no major reports of anyone having serious adverse reactions to it. “But if anyone is really developing any sort of symptoms that are at all concerning to them and they’re worried, it’s best to reach out to a healthcare provider and let them know what’s going on,” Dr. Russo says.

Dr. Russo stresses that the vaccine “has been well-tolerated,” adding, “the benefits far, far outweigh any potential risks.”

Who should get the mpox vaccine?

The CDC lists the following people as having high potential for exposure to mpox, and should be offered the vaccine:

  • People who had known or suspected exposure to someone with mpox.

  • People who had a sex partner in the past two weeks who was diagnosed with mpox.

  • Gay, bisexual, and other men who have sex with men, and transgender or nonbinary people (including adolescents who fall into any of these categories) who, in the past six months, have had:

  • People who have had any of the following in the past six months:

  • People who are sex partners of people with the above risks.

  • People who anticipate experiencing any of the above scenarios.

  • People with HIV infection or other causes of immunosuppression who have had recent or anticipate potential mpox exposure.

  • People who work in settings where they may be exposed to mpox.

How do you protect against monkeypox?

Experts say that monkeypox isn’t something the general public should worry about at this point. “It is not very contagious outside of close contact,” Dr. Adalja says. But, he adds, “if someone thinks they are at risk for monkeypox because of their activities and exposures, they should seek vaccination either before they engage in those activities or after they have been exposed.”

The CDC also recommends the following to protect against monkeypox:

  • Avoid close, skin to skin contact with the monkeypox rash.

  • Don’t handle or touch the bedding, towels, or clothing of a person with monkeypox.

  • Wash your hands often with soap and water or use an alcohol-based hand sanitizer, especially after contact with sick people.

Is there a cure for monkeypox?

There is not a cure for monkeypox, but there doesn’t really need to be, Dr. Schaffner says. “For the most part, this is a self-limiting infection and all of these lesions resolve over a period of two to four weeks,” he says. “Most people recover without specific therapy.”

However, antiviral medications like tecovirimat (TPOXX) may be prescribed for people who are immunocompromised or more likely to get severely ill from monkeypox, he says.

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