Before 2022 most people had not heard of monkeypox virus. At that time, the virus began to spread across continents, including to places that it was not historically found. The virus caught the attention of scientists at that time because of changes to the way it was transmitted and unusual symptoms that were occurring. When they studied these changes, scientists found that the time interval between exposure to the virus and development of symptoms had shortened. Since 2022, different versions of monkeypox virus, known as clades, have been causing disease in countries around the world. While the spread has slowed in the U.S., small numbers of cases are still diagnosed. But, by late 2025, the largest number of cases were occurring in several African countries.  

The disease

What is mpox?

Mpox is an infection caused by monkeypox virus. This virus was first discovered in monkeys in research facilities in Denmark in 1958. The first person diagnosed with mpox was a 9-month-old baby in the Democratic Congo of the Republic in 1970.Monkeypox is an orthopox virus that is closely related to the virus that causes smallpox. 

People with mpox can experience a range of symptoms from none to mild symptoms with rash. When people develop symptoms, they often start with: 

• Fever
• Fatigue
• Headache
• Weakness
• Enlarged lymph nodes 

Shortly after these symptoms start, a rash develops. The rash can be anywhere on the body, but most often, it occurs on the face, arms and legs, including the palms of the hands and soles of the feet. The skin lesions look like blisters or sores and can be deep in skin. They are painful and become itchy as they heal. The lesions can last for two to four weeks.

Severe cases of mpox include more painful lesions that appear in the mouth, genital area, or anal area. The pain can limit the person’s ability to eat, urinate, or have a bowel movement. Ulcers can go through the layers of skin and infect the muscles below, leading to death of that area of muscle. In rare cases, the deep skin lesions require specialized wound care, such as the types of treatments commonly used for severe burns. 

Other complications can include: 

• Inflammation in the brain (encephalitis)
• Inflammation of the heart (myocarditis or pericarditis)
• Development of ulcers in the gastrointestinal tract that cause abnormal narrowing of the organs involved in digesting food. 

Life-threatening complications can include bloodstream infections (sepsis) or excessive bleeding, known as hemorrhaging. People who are immune suppressed are more likely to experience severe disease and complications. 

Infection with one type of monkeypox virus provides immunologic memory that is protective against other types of the virus. So, if someone is infected in the future, they are unlikely to experience severe disease. 

How do you catch mpox?

Mpox infections are most often spread through contact with body fluids containing monkeypox virus or the fluid from lesions. Less commonly, monkeypox virus can spread through contact with objects and surfaces that have not been disinfected after use by someone with mpox. This can include clothing, bedding, towels, or other items or surfaces that have come in contact with mpox lesions, fluid from lesions, or body fluids that contain the virus. People can spread the virus to others from up to four days before they develop symptoms until the skin lesions have completely healed (i.e., a new layer of skin has developed).   

Two other notes about spread of mpox:

1. Women can spread the virus to their unborn babies, and this can result in fetal death.
2. Infected animals can spread the virus to people. They can be infected through bites or scratches, eating meat from infected animals, or from contact with animals, such as from hunting, trapping, cooking, or other activities involving handling animals.

How common is mpox?

A global outbreak of mpox began in 2022. Cases in the U.S. increased rapidly through August 2022. Since that time, cases have continued to occur, but at a slower pace. By late 2025, cases were more common in several countries in Africa, but because of international travel and low levels of continued spread, cases occur in many countries, including in the U.S. 

While certain groups are at higher risk, anyone can get mpox if exposed to someone who is infected. Those considered to be higher risk, include:

• Healthcare workers and others who may come into contact with the virus through their job, like those who work in labs, first responders, and environmental service workers in places with infected people
• People who live with or are in close contact with infected individuals, including children
• People with multiple sexual partners, including men who have sex with men; gay, bisexual, and transgender people; and sex workers and their clients

The vaccine

The mpox vaccine is recommended only for individuals at high risk of infection. The vaccine is given in two doses separated by four weeks, and it is typically injected into the fatty tissue above the muscle. This is known as a subcutaneous injection. However, it has also been given in the tissues under the skin, known as an intradermal injection. (See “How is this vaccine given?” in the “Other questions you may have” section of this page for more information.)

People with ongoing risk based on their job may be recommended to get booster doses. The timing of these doses depends on their risk.

How is the mpox vaccine made?

Jynneos is a live weakened viral vaccine. However, it is unique from other vaccines of this type. Although the virus is live, it has been modified so that it cannot replicate in a person’s body. 

While there is another vaccine for the prevention of orthopox viruses, including monkeypox and smallpox, it causes more side effects than Jynneos. Known as ACAM2000, this vaccine is not regularly used, but it is available in the government stockpile in the event that it would be needed in an emergency, such as if smallpox was introduced during a bioterror event. 

Does the mpox vaccine work?

Two doses of Jynneos vaccine are recommended to provide strong and consistent protection. The doses should be separated by four weeks, with maximum protection developed by two weeks after the second dose. Small initial studies suggested that six to eight out of every 10 vaccinated people will be protected against infection. Larger studies are ongoing to determine how effective the vaccine is in the larger, more diverse population.  

What are the side effects of the mpox vaccine?

Vaccine side effects include those that may occur with any vaccine, such as pain, redness and itching at the vaccination site or an allergic reaction to the vaccine or a component of it. 

Some people can also experience: 

• Fever
• Headache
• Tiredness
• Nausea
• Chills
• Muscle aches

Other questions you might have

How is this vaccine given? 

The mpox vaccine can be given in one of two ways. Both require a shot: 

• In the fat layer below skin: Known as a “subcutaneous injection,” this is the administration method used for clinical testing of the vaccine; therefore, it is the preferred method for administration. In this method, the needle is placed far enough into the skin to reach a fat layer below and is typically given on the back of the upper arm. Since immune system cells are present in this layer, a sufficient immune response develops, and injection site side effects are uncommon. This method rarely leaves a mark on the skin. It is also the preferred method for people with skin prone to developing keloid, or raised, scars.
• Between layers of skin: Known as “intradermal injection,” with this method the needle only penetrates the top layers of skin, either on the forearm or below the shoulder blade. The tissue under the top layer of skin has many immune cells, making it a useful site for vaccine administration because a smaller amount of vaccine can be used and still lead to a strong immune response. This approach also tends to be less painful; however, it can leave a mark, and side effects at the injection site tend to be more frequent than following subcutaneous administration. 

Where can I find an mpox vaccine? 

Mpox vaccine availability varies by region. In some large cities, the vaccine may be available at several locations, including from individual healthcare providers, health departments, public health clinics, and even at some social gatherings. In other areas, the vaccine may only be available through the health department. Check with your healthcare provider or your local health department. 

Can I get the mpox vaccine after I have been exposed? 

Yes. The mpox vaccine can be given before or after exposure to monkeypox virus. If a person has been exposed to monkeypox virus, the vaccine should be given within four days of exposure. 

Can the vaccine be given to pregnant people, breastfeeding individuals, or children?

Jynneos can be given to people who are pregnant or breastfeeding. 

This vaccine is only approved for use in those 18 years of age and older. However, some children have been exposed to the virus. The most common source of exposure for children under 12 has been via close physical contact with a household member. Among those older than 12, the most common exposure during adolescence has been through intimate male-to-male contact. Even though the mpox vaccine is not approved for those younger than 18 years of age, children at high risk for mpox can get it under emergency use authorization (EUA). 

Relative risks and benefits

Do the benefits of the mpox vaccine outweigh its risks?

The mpox vaccine can cause mild side effects. On the other hand, clusters of symptomatic mpox disease continue to occur among certain groups in populations throughout the world. 

Disease risks

• Fever
• Fatigue
• Headache
• Weakness
• Enlarged lymph nodes
• Painful and itchy rash causing open sores
• Painful lesions in the mouth, genitals or anal area
• Complications including inflammation of the heart or brain, ulcers that cause constriction of the digestive organs, bloodstream infections or hemorrhaging
• Death 

Vaccine risks

• Pain, redness and itching at vaccination site
• Fever
• Headache
• Tiredness
• Nausea
• Chills
• Muscle aches
• Allergic reaction 

References

World Health Organization. Mpox (Monkeypox).