You Most Likely Won't Need the Mpox Vaccine

After more than two years of battling COVID-19, the unusual mpox (formerly known as monkeypox) outbreak is triggering another wave of anxiety.

But for now, health experts have reiterated that most people in the United States do not need to worry about being seriously ill with mpox, or getting vaccinated against it.

“I want to stress this is not something that we’ll be vaccinating the general population for," said Aaron E. Glatt, MD, MACP, FIDSA, FSHEA, chief of infectious diseases at Mount Sinai South Nassau Hospital in Oceanside, New York.

Mpox is a rare disease, with only nine confirmed cases in the U.S. so far. Unlike COVID-19, mpox leaves very visible rashes on the skin, which makes it easier to contact trace.  

“Everybody's terrified that this could be another COVID-like illness. That will not happen,” he said.

What Vaccines Exist for Mpox?

The U.S. has a stockpile of more than 100 million doses of the original smallpox vaccine, called ACAM2000. It’s a live virus vaccine that is 85% effective at preventing mpox, per the Centers for Disease Control and Prevention (CDC).

However, ACAM2000 is only licensed to prevent smallpox. This vaccine is associated with some rare side effects and shouldn’t be given to certain patients, including those who are immunocompromised, are infected with HIV, or have certain skin conditions, including eczema.

“The vaccine possibly would be more damaging than the very, very low likelihood that somebody's going to get the disease,” Glatt said. “You don't want to give this vaccine to people who may not get the disease.”

A second vaccine, called Jynneos, was approved in 2019 for the prevention of both smallpox and mpox. There are more than 1,000 doses of this vaccine in the stockpile.

Some people who have been exposed to mpox may be vaccinated. And those who work in high-risk environments—like certain laboratory and healthcare professionals—may receive the shot.

But getting the vaccine requires special permission from the CDC, said Stanley Deresinski, MD, FACP, FIDSA, an infectious disease expert and professor of medicine at Stanford University.

Due to the limited number of cases and relatively small vaccine supply, Deresinski said the CDC may use a strategy called “ring vaccination” that was used to eradicate smallpox in the mid-1900s. By vaccinating all the people with potential exposure to an infected person, health officials aim to stop the disease from spreading without vaccinating the whole population.

“There's no indication for mass vaccination at this time,” Deresinski said.

Bavarian Nordic, the company that makes Jynneos, said it will ramp up production of the vaccine to support the global mpox response. Jennifer McQuiston, DVM, MS (CAPT, USPHS), deputy director of the Division of High Consequence Pathogens and Pathology at the CDC, told reporters that some doses have already been requested to immunize high-risk contacts of the individuals who are currently sick with mpox.

The U.S. also has more than two million doses of an antiviral pill called Tecovirimat used to treat smallpox. Deresinski said the drug is well tolerated and safe.

Is Mpox Related to Smallpox?

Mpox is closely related to smallpox. It was first discovered in 1958 in monkeys used for research, but it is now spread mostly by rodents. The recent uptick in mpox cases in Africa and worldwide may be due in part to the waning immunity to smallpox since most countries stopped their vaccination programs in the 1970s and 1980s.

The smallpox vaccine, created in 1796, was the first successful vaccine against a contagious disease. Thanks to a global effort in the mid-20th century, cases of smallpox were eliminated worldwide. No one has become naturally infected with smallpox since 1977, the CDC said.

Older adults may have residual immunity to smallpox from being vaccinated as children and young adults. It’s not clear how long this initial immunity lasts, though one study indicates antibodies may protect against smallpox for up to 88 years.

Some military service people are still vaccinated against smallpox. The U.S. has maintained an emergency supply of smallpox vaccine partially due to the risk of a bioterrorism attack involving the virus.

How Can You Protect Yourself Against Mpox?

Mpox is spread through close physical contact with people who are infected. This could mean sharing a bed, touching someone with wounds, or inhaling respiratory droplets from an infected person.

Many of the initial infections reported in Europe were among men who have sex with men. But the virus is not sexually transmitted in the traditional sense, but rather by close physical contact, making other groups vulnerable to infection, John Brooks, MD, chief medical officer for the CDC's Division of HIV/AIDS Prevention, told reporters at a media briefing.

People who become sick with mpox should stay isolated at home and avoid contact with people, especially those who are immunocompromised, pregnant, or otherwise at high risk.

“In the absence of close physical contact with someone, the likelihood of getting infected is exceedingly low,” Deresinski said.

Glatt added that continuing normal hygiene—like practicing good hand washing and minimizing contact with sick people—is sufficient to minimize exposure to the disease.

“The general population should take a deep breath and not be worried about this,” Glatt said.

“It's a very important issue for public health officials, for the CDC, for hospitals and for epidemiologists to make sure that we keep everybody as safe as possible,” he added. “But you're not going to get this sitting in the waiting room, library, in the hospital or another place.”