Mpox: What You Need to Know

[Originally published: July 11, 2022. Updated: Oct. 28, 2025.]

Mpox, formerly known as monkeypox, has raised alarm in recent years after a global outbreak began in 2022. Since then, this infectious disease, which is typically found in parts of Central and Western Africa, has occurred in countries where it’s not normally seen.

The 2022 outbreak led to more than 90,000 cases worldwide, including more than 32,000 in the United States. It was caused by a strain called Clade IIb, while most recently reported cases are caused by Clade I, a strain that can cause more severe illness and lead to death in up to 10% of those infected.

Although it can affect anyone, most mpox cases from the 2022 outbreak were sexually transmitted and associated with men who have sex with men. For reasons not yet known, the virus is behaving differently than it did in the past. For example, before 2022, mpox was not known to spread easily among people or to infect large groups at once. Now, it can spread through close contact.

In October 2025, several cases of the Clade I strain were detected in California residents who had not traveled abroad and did not have contact with one another.

Similar to smallpox, but less severe, mpox was discovered in 1958 when two outbreaks of a pox-like disease occurred in colonies of monkeys kept for research in Denmark, according to the Centers for Disease Control and Prevention (CDC).

Despite being originally called “monkeypox,” the source of the disease is not known. However, African rodents and non-human primates, like monkeys, may carry it and infect humans. The first human case was reported in 1970 in the Republic of the Congo. “The disease has been renamed ‘mpox’ to avoid prejudiced and stigmatizing connotations related to the original name,” says Lydia Aoun Barakat, MD, a Yale Medicine infectious diseases specialist.

Until 2022, nearly all cases in people outside of Africa were linked to imported animals or with travel to other countries where the disease is common.

Normally, someone infected with mpox first presents with a nonspecific flu-like illness, including fever, headache, and malaise, Dr. Barakat says. “Swollen lymph nodes can be a telltale sign, after which a rash appears. The rash usually starts off like several spots that progresses over time to the classic mpox lesions.”

The lesions, which fill with cloudy fluid, remain for five to seven days before beginning to crust. They typically scab over by the end of the second week and remain for about another week before starting to fall off. An infected person is contagious from the start of the flu-like symptoms until all scabs have fallen off.

“The rash traditionally seen with mpox starts in the center of the body, the face, or the head, and then moves outward to the extremities. That is the classic presentation,” Dr. Barakat says. “But with the 2022 worldwide outbreak, it did not always follow this pattern. In many cases, lesions were only seen in the genital area or around the anus. It’s important to recognize that these lesions could be mistaken for sexually transmitted diseases, such as syphilis or herpes, which can occur in these areas of the body.”

Those infected might develop a rash as the only symptom of the disease. Others may get a rash first, followed by other symptoms. Most illnesses clear up in two to four weeks.

If you have new or unexplained rashes, sores, or other symptoms, you should see your health care provider.

Mpox can spread in different ways. Before the 2022 outbreak, the most common method was by direct contact with infected animals by way of a bite, scratch, or feces, or by preparing/eating meat or using products from an infected animal.

In the past, human-to-human transmission was rare, Dr. Barakat says.

What was troubling about the 2022 cases is that mpox appeared to be spreading through close contact with an infectious rash, scab, or bodily fluids. It can also be transmitted through respiratory secretions during prolonged face-to-face contact or during intimate physical contact, including kissing, cuddling, or sex. It is not yet known if it can spread through semen or vaginal fluids.

Additional transmission can occur from touching clothing, linens, or other items that came in contact with an infectious rash or body fluids. Pregnant women can also transmit the virus to their fetus.

There are several different ways people can prevent mpox infection, including avoiding close, skin-to-skin contact with a mpox rash; not handling or touching bedding, clothing, or towels of a person who has mpox; and washing hands often with soap and water or using an alcohol-based hand sanitizer, especially after contact with people sick with the virus.

Individuals who are at increased risk (men who have sex with men with certain high-risk sexual exposures) are encouraged to receive two doses of the Jynneos vaccine. Vaccination reduces the chances of contracting the infection and of severe illness, hospitalization, and death. Vaccination is also an important tool in preventing the spread of mpox.

Yes. According to the CDC, mpox can spread to anyone through close, personal, skin-to-skin contact, which can also happen when you have sex. Examples include:

• Oral, anal, and vaginal sex or touching the genitals (penis, testicles, labia, and vagina) or anus of a person with mpox
• Hugging, massage, and kissing
• Touching fabrics and objects that were used by a person with mpox and that have not been disinfected, such as bedding, towels, fetish gear, and sex toys

Doctors can suspect mpox based on a patient’s history and a physical exam; anyone who suspects they might have the virus should contact their health care provider. The diagnosis can be confirmed with an mpox PCR test of the lesion that is available at specialized labs.

Those who are sick with mpox should isolate at home. For those with an active rash or other symptoms, stay in a room or area separate from family and pets when possible.

While there are no specific treatments for mpox infections, antiviral drugs licensed for smallpox use are effective and can be used against mpox. These might be advised for people more likely to get very ill, including those with weak immune systems.

Two vaccines licensed by the Food and Drug Administration against smallpox are available for preventing mpox. Jynneos is a two-dose vaccine (separated by four weeks), which is up to 85% effective in preventing mpox after two doses and is recommended for those who are at increased risk of exposure to mpox and those who have been exposed to mpox in the past two weeks.

The other vaccine, called ACAM2000, is a modern iteration of an old smallpox vaccine. The WHO celebrated the eradication of smallpox in humans in 1980. Now stored in a national stockpile, the vaccine has been used for mpox, but there are drawbacks: it can lead to serious illness in people with compromised immune systems. It is not the preferred vaccine for mpox at this time.

“Viruses need a host to survive and replicate. With climate change and the disruption of the ecosystems, infectious agents might undergo genetic or behavioral changes in order to survive. A new or drastically changed virus can cause severe illness in a susceptible host with no previous immunity,” Dr. Barakat says. “As humans, we need to be aware of the environment and use prevention as the best medicine through evidence-based science and research.”