What to Know About Risk in U.S.

Mpox is a member of the Poxviridae family of viruses called Orthopoxvirus, with smallpox, vaccinia, and cowpox among its ranks.

As such, smallpox vaccination is highly effective against mpox, explained Monica Gandhi, MD, MPH, professor of medicine at the University of California, San Francisco.

Mpox was first discovered in monkeys in the DRC in 1958, with the first documented human case occurring in 1970 during a period of intensified efforts to eliminate smallpox in this region.

Multiple mpox outbreaks have occurred in West and Central Africa in the past decade in areas where the virus is considered “endemic” (circulating at a low level), Gandhi said.

“Infection in endemic regions is generally spread [to humans] by rodents, such as rats, mice, and squirrels, and prior to the global outbreak of 2022, was usually detected in the U.S. only among returning travelers from these regions,” Gandhi told Healthline.

“There was a human outbreak in the U.S. in 2003 from pet prairie dogs infected by a shipment of mammals from Ghana,” she noted.

However, this epidemiology shifted with the 2022 outbreak (clade II), which had a lower fatality rate than prior outbreaks. The first case of mpox among men who have sex with men (MSM) was reported to the WHO on May 13, 2022. Mpox is not to be mistaken with a sexually transmitted infection (STI).

“The 2022 global outbreak caused more than 99,000 cases in 116 countries,” Gandhi said. “That particular global outbreak ended likely due to a combination of natural immunity and mass vaccination for the virus with the Jynneos vaccine (the former smallpox vaccine which works well against mpox),” she explained.

The current clade 1b outbreak, however, appears to be more easily transmissible and lead to more severe symptoms. Clade 1b also has a higher fatality rate than clade II, Gandhi noted.

“The WHO is appropriately concerned about this severe outbreak, which is now affecting a lot of children due to routine contact spreading the virus,” Gandhi said.

The clade II outbreak led to more than 30,000 cases in the U.S., with New York and California declaring states of emergency in 2022.

At present, no cases of clade 1b have been reported in the U.S., and the CDC maintains the risk to the U.S. is very low. A small number of clade II cases have been reported since the 2022 outbreak.

“The new clade of mpox outbreak is limited to a few countries around the world,” Will Kimbrough, MD, a primary care physician at One Medical,” told Healthline.

“With there being some pre-existing immunity from past cases and at-risk individuals having already received the 2-part vaccine series in 2022, it’s unlikely that we’ll see as large of an outbreak again in 2024. Individuals should talk with their primary care provider if they need guidance on risk reduction approaches,” Kimbrough said.

The low risk to the U.S. may be ascribed to a lack of direct flights from the U.S. to the DRC and neighboring African countries, noted David Diemert, MD, professor in the School of Medicine & Health Sciences Department of Medicine at George Washington University.

“However, if the outbreak continues to spread in Africa, or if additional cases are detected in Europe or other continents, this assessment may change,” Diemart told Healthline.

Mpox spreads from person to person through direct skin contact, often occurring in the home or within healthcare settings. Symptoms of mpox may include:

• rash (i.e., face, genitals, mouth, hands, feet, or chest)
• respiratory symptoms (i.e., sore throat, cough, and nasal congestion
• fever, chills, and body aches
• headache and fatigue
• swollen lymph nodes

“Within 7 to 14 days of exposure, infected individuals typically experience flu-like symptoms, Kimbrough said. “Within 1 to 3 days of having a fever, people develop a rash, which can appear as raised, pearly, fluid-filled blisters.”

The rash, Kimbrough explained, may last for 2 to 4 weeks before forming scabs and healing. “An individual with mpox is no longer considered contagious once all the scabs have fallen off and new skin has formed,” he said.

People who travel to affected areas may risk exposure to mpox. If you believe you’ve been exposed, Kimbrough recommends the following protocol:

• Isolate immediately. Follow the CDC’s guidelines for infection control.
• Reach out to your healthcare team if you have associated symptoms (body aches, fatigue, fever, headache, swollen lymph glands). “Your healthcare provider can help you with a plan to determine whether your symptoms are due to mpox or other causes,” Kimbrough said. “They can discuss with you how to take care of yourself while you’re sick, and arrange for testing.”
• Notify anyone you’ve been in close contact with since your symptoms began.

Many cases of mpox resolve on their own without medical treatment.

Currently, there are no approved treatments for severe cases of mpox, but antiviral drugs that were developed to treat smallpox may help treat severe illness. These treatments, however, may not be effective against new strains.

One such antiviral treatment, tecovirimat, didn’t seem to work well against clade 1b, a recent study found.

“If you’re not sure if antiviral treatment is right for you, please reach out to your healthcare provider,” Kimbrough said.

For those with less serious mpox infection, Kimbrough recommended the following at-home treatments:

• pain relievers or fever reducers (i.e., acetaminophen or ibuprofen)
• sitz baths to soothe lesions in the genital area
• calamine lotion for itching or painful sores
• rest and fluids to prevent dehydration

The current Jynneos vaccine is highly protective against all clades of the mpox virus.

“Part of the WHO’s motivation in declaring this emergency is to get vaccines mobilized to provide to Africa to stem the outbreak there, which will keep the rest of the world safe as well from further spread,” Gandhi said.

However, the mpox vaccine is not widely available in the African countries currently experiencing the clade 1b outbreak, Diemart noted.

Vaccination against mpox is advised for anyone at increased risk of exposure, including:

• Individuals who have had a known exposure to someone with mpox.
• Men who have sex with men, including gay or bisexual people who had intercourse with more than one partner. within the past 6 months, or who’ve had sex with more than 1 partner, or who had a new diagnosis of an STI).
• People who’ve had intercourse at a commercial sex venue (i.e., sex club or bathhouse).
• Anyone with occupational exposure to mpox; or who had sex at a commercial sex venue (i.e., a sex club or bathhouse).

“In the U.S., the CDC recommendations for vaccination are unchanged since the start of the 2022 outbreak that has primarily affected men who have sex with men,” Diemart said.

The growing mpox outbreak across the African region prompted the WHO to declare a global public health emergency.

After the first European case of mpox was reported in a Swedish citizen, a WHO official announced the virus is unlikely to trigger another pandemic, dispelling any misinformation about the outbreak.

While further transmission of mpox in Europe is likely, the risk to the U.S. remains very low. People considered at high risk for mpox infection should receive the Jynneos vaccine.