A global outbreak caused by monkeypox virus began in 2022, catching the attention of the public because of its spread across continents, including to places that did not historically report mpox cases. It also caught the attention of scientists because of changes to the way it was transmitted and unusual symptoms. Subsequent studies have also determined that the time interval between exposure to the virus and symptoms has shortened. Ongoing global transmission led to more than 90,000 cases by the spring of 2023, and monkeypox virus continues to circulate.  

The disease

What is mpox?

Mpox is an infection caused by monkeypox virus. This virus was first discovered to cause disease in 1958. Part of the poxviridae family, monkeypox is an orthopox virus that is closely related to the virus that causes smallpox. At least two versions, or variants, of the monkeypox virus are causing illness. 

People with mpox can experience a range of symptoms from none to mild symptoms with rash. Most commonly, people with symptoms start with fever, fatigue, headache, weakness and enlarged lymph nodes. Shortly after, people develop a rash that can be anywhere on the body but most commonly is 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. 

Severe cases of mpox include more painful lesions that appear in the mouth, genital area, or anal area, limiting the affected individual’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 scenarios, the deep skin lesions require specialized wound care, such as the types of treatments common for severe burns. Other severe cases can lead to complications like inflammation in the brain (encephalitis) or heart (myocarditis or pericarditis), or 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 provides immunologic memory that is protective against severe disease during future infections, regardless of strain. 

How do you catch mpox?

Mpox infections are most often spread through contact with body fluids containing the 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 items like clothing, bedding, towels, or other items or surfaces that may have come in contact with the lesions, fluid from the lesions, or body fluids that could contain the virus. People can be infectious up to four days prior to developing symptoms and remain infectious until the skin lesions have completely healed (i.e., a new layer of skin has developed).   

How common is mpox?

Beginning in 2022, there was a global outbreak of mpox. Cases in the United States increased rapidly through August 2022. Since that time, cases have continued to occur, albeit at a slower pace. Public health efforts, including identifying populations who would benefit from vaccine, have been informed by the need to prioritize people most likely to be infected. However, anyone, regardless of sexual orientation, sexual practices, age or gender can get mpox if exposed to someone who is infected.

The vaccine 

While a vaccine is now available, it is recommended only for individuals at high risk of infection, including: 

1. People who work with monkeypox virus or who are at risk of exposure to the virus due to their occupation (e.g., laboratory workers who test for or work with the virus, healthcare workers who treat infected patients, environmental services workers in areas where infected patients are staying, first responders during an outbreak, among others)
2. People who have had a known or suspected exposure or who were intimate with someone diagnosed with mpox during the two weeks prior to their diagnosis
3. People 18 years and older at risk due to increased spread through intimate contact, including gay, bisexual and other men who have sex with men, and transgender or nonbinary people who have had one of the following in the past six months:
   1. A new diagnosis of at least one sexually transmitted disease
   2. More than one partner
   3. Intimate encounters at commercial sex venues
   4. Intimate encounters in association with large public events in geographic regions where the virus is circulating
4. Intimate partners of individuals described in bullet point #3 or anyone who anticipates being part of the group listed in #3 or an intimate partner of someone in that group 

How is the mpox vaccine made?

Jynneos is a live weakened viral vaccine. However, it is unique from other vaccines of this type because although the virus is live, it has been modified so that it cannot replicate in a person’s body. While there is another vaccine available for the prevention of orthopox viruses, including monkeypox and smallpox, it has not been used in the current outbreak because it has more side effects than Jynneos. 

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 people vaccinated will be protected against infection; bigger 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 also experience fever, headache, tiredness, nausea, chills and muscle aches. Individuals who receive the vaccine under the skin, called intradermal administration, typically have less pain but more side effects at the injection site, like itching, swelling, redness and thickening of the skin. For more information on intradermal administration, see “How is the vaccine given?” in the “Other questions you might have” section of this page.

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. The Centers for Disease Control and Prevention (CDC) offers an mpox vaccine locator on this page of their website.

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.

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

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

Very few children had mpox during the 2022 outbreak and period of ongoing community transmission in the United States. Further, the 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. 

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, 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

Centers for Disease Control and Prevention. Mpox. 

World Health Organization. Mpox (Monkeypox).