Diana Zuckerman, Ph.D., Thomas Eagen, Ph.D., & Sophia Phillips, M.S.
Updated September 30, 2022
What is monkeypox (mpox)?
Mpox is a disease caused by an infection with the monkeypox virus. It is in the same family as the smallpox virus called variola. Although first discovered in monkeys in 1958 and seen in humans starting in 1970, the current outbreak has spread rapidly across continents for the first time. The first U.S. case was seen on May 18, 2022 and by July 23, the World Health Organization Director-General had declared the mpox outbreak a Public Health Emergency of International Concern. The Biden Administration declared mpox a Public Health Emergency on August 4, 2022. As of September 30, 68,428 cases have been reported worldwide with 25,851 of those cases occurring in the U.S.
It is life threatening?
Mpox is usually mild, and most people recover within a few weeks without treatment. A tiny fraction of 1% of the people diagnosed with mpox have died in the 2022 outbreak, which is typical of the West African strain that is currently circulating. As of September, 2022 there have been a total of 28 deaths globally, with 2 occurring in the United States.
Who is at a greater risk of infection?
The current mpox outbreak has disproportionately affected certain populations:
- Men who have sex with men (according to the CDC 98.2% of reported cases in the U.S. are male)
- People who are immunocompromised
- Elderly individuals
- Young children under eight years of age
- Pregnant people
- Individuals with a history of skin diseases such as atopic dermatitis or eczema
- Healthcare workers caring for patients confirmed or suspected of mpox
How does it spread?
Mpox spreads through close physical interactions between people, such as direct contact with a person who has mpox’s rash, scab, or body fluid; touching shared contaminated surfaces; and through respiratory droplets from coughs and sneezes. To prevent the spread of the disease, there are many steps you can take to protect yourself from mpox including:
- Avoid close contact (within three feet) with people who have been infected with mpox and their belongings. This includes bedding and towels of infected individuals.
- Wash your hands frequently with soap and water or use an alcohol-based hand sanitizer.
- Wear face coverings and other protective gear such as gloves when interacting with someone who has mpox symptoms.
- Be aware of symptoms if you are sexually active, disclose any recent/current diagnoses or symptoms of sexually transmitted infections with potential partners, and limit your number of sexual partners.
- Seek care if you develop symptoms and get vaccinated if you are at risk.
Myths and reality
A major misconception is that mpox is spread solely through sexual contact. Although sexual contact is a major factor in the current outbreak, mpox can spread in other ways, including any form of direct contact. And although the current outbreak has affected the LGBTQ+ community heavily, everybody is at risk for mpox, and it can affect anyone who is in close contact with contagious individuals.
What are the symptoms?
If you get infected with mpox, it usually takes between 5-21 days for the first symptoms to appear. The first symptoms include a high temperature, headache, muscle aches, swollen glands, shivering, and exhaustion. A rash will appear one to five days after the first symptoms. The rash often starts on the face, and then spreads to other parts of the body. The rash appears as raised bumps that turn into small blisters filled with fluid. The blisters will form scabs and fall off. The symptoms typically will clear up in a few weeks. While you have symptoms they can be spread to other people. These are the major symptoms:
- Muscle Aches
- Swollen Lymph nodes
Is there a vaccine for mpox?
In the U.S., two vaccines may be used to prevent mpox disease:
- JYNNEOS was initially approved by FDA in September 2019 for the prevention of smallpox and mpox disease in adults over 18 who are determined to be at high risk. This initial approval required all vaccinations to be subcutaneous (into the fat layer). JYNNEOS was awarded an Emergency Use Authorization (EUA) on August 9, 2022, for the same indication but instead using an intradermal injection (into the skin layer). The EUA also allows people under 18 to take the vaccine if they are at high risk.
Current dosing with JYNNEOS requires two intradermal injections for people over 18 and two subcutaneous injections for people under 18. These injections consist of live vaccinia virus and are given four weeks apart. It is important to know that people can be vaccinated after exposure to mpox virus to help prevent mpox disease. The Centers for Disease Control (CDC) recommends the vaccine be given within four days from the date of exposure to prevent infection. If given between 4-14 days after exposure, it may reduce symptoms. Normal side effects of the vaccine include pain at the injection site, swelling, fatigue, muscle pain, nausea, headaches, and chills. Individuals who take JYNNEOS are not considered fully vaccinated until two weeks after their second dose.
The FDA approval of JYNNEOS against smallpox was based on 22 clinical trials involving a total of 7,871 adults ages 18 through 80 years who received at least 1 dose. Those trials included two Phase 3 studies, both of which showed the vaccine was similarly effective in terms of immunogenicity compared to another smallpox vaccine, ACAM2000. The safety of JYNNEOS was evaluated in unvaccinated or non-immune healthy adults; in healthy adults previously vaccinated with a smallpox vaccine; in HIV-infected adults; and in adults with atopic dermatitis.
The FDA approval of JYNNEOS against mpox was based on survival data of non-human primates that were intentionally infected with mpox virus. Approximately 80-100% of JYNNEOS-vaccinated animals survived, compared to 0-40% of non-vaccinated animals. This fatality rate seems high for the vaccinated and non-vaccinated animals, which may be due to the earlier strain of mpox being more lethal than the current strain. A December 2022 CDC evaluation of one million JYNNEOS does given in the U.S. between May 22–October 21, 2022, further supported the vaccine’s safety, consistent with prelicensure studies. The most common adverse health events reported were not serious and included injection site reactions. Serious adverse events were rare among adults, and no serious adverse events were identified among persons over 18 years of age.
- ACAM2000 vaccine was approved by FDA for immunization against smallpox disease in August 2007, for persons aged 1 year or older. It was made available for use against mpox under an Expanded Access Investigational New Drug (EA-IND) protocol. This requires informed consent from the patient and other requirements for use.
Vaccination with ACAM2000 requires one injection of a live virus that pricks the skin. The virus growing at the site of this inoculation lesion can be spread to other parts of the body or even to other people. Individuals who are vaccinated with ACAM2000 must take precautions to prevent the spread of the vaccine virus and are considered protected after 28 days. ACAM2000 is associated with more severe, rare side effects compared to JYNNEOS vaccines, such as death of tissue cells on the surface of the skin, painful rashes and fever, and inflammation of the heart muscle. All of these can be fatal.
According to preliminary data from the CDC, people who were eligible for a mpox vaccine but did not receive one were about 14 times more likely to become infected than those who were vaccinated. However, this is based on individuals who have taken just one dose of the vaccine. Additionally, it not not possible to distinguish how much of the additional protection is due to behavioral changes and how much is due to the vaccine alone, among at-risk populations.
How are vaccines distributed?
The vaccines currently being administered are from emergency stockpiles created to respond to sudden release of smallpox. As of August 29, 2022, approximately 1 million vials of JYNNEOS have been allocated nationally. The U.S. has one of the largest vaccine stockpiles, and ordered an additional 2.5 million doses on July 1, 2022 in response to the outbreak. The U.S. government supply is expected to reach approximately 7 million vials by mid-2023. The ACAM2000 vaccine is more available but demand is minimal due to the significant side effects.
The EUA for JYNNEOS that switched to intradermal injection increased the total number of doses available five-fold, because only one fifth of the volume of vaccine is required to achieve the same level of immune response.
What do you do if you develop symptoms or think you may have been exposed?
If you have had close contact with someone who has mpox or an environment that may have been contaminated with the virus, monitor yourself closely for signs and symptoms for 21 days after the time you were last exposed. Limit close contact with other people as much as you can. If you think you have symptoms of mpox, contact your healthcare provider for advice, testing, and medical care. In order to be tested you must have a visible rash or lesion. A healthcare provider will use a swab to take a specimen for lab testing. PCR testing became available on July 13, 2022, through an emergency use authorization (EUA) awarded to Quest Diagnostics, and on October 7, 2022, FDA also issued an EUA to Abbott Molecular for their PCR test.
Until you receive your test result, isolate yourself from others if possible. Clean your hands regularly. If you have a positive test for mpox, your healthcare provider will advise you on whether you should isolate at home or in a health facility, and what care you need.
What are the treatments?
Mpox is usually mild, and most people will recover within a few weeks without treatment. However, if symptoms persist, you may need treatment in the hospital. Those most at risk of severe infection include older people, young children, and people with a weakened immune system.
Tecovirimat (also known as TPOXX) is an antiviral drug that is used in the treatment of mpox. It was initially approved for the treatment of smallpox under a regulation known as the “Animal Rule.” The Animal Rule determines whether a drug is effective based on well-designed studies in animal models of a human disease. Safety must be evaluated in healthy human subjects, however. Since smallpox has been eradicated, efficacy studies in humans would not be ethical or feasible, which is why the Animal Rule is the basis for approval. There are reports of using tecovirimat as a treatment for mpox in west and central Africa, but there are not enough data to demonstrate how well it worked. Tecovirimat has been shown to be effective in animal models of mpox and is reasonably safe when studied on healthy people. The CDC Expanded Access Investigational New Drug (EA-IND) protocol allows for the use of tecovirimat as an experimental treatment for mpox, but it is not approved by the FDA for that purpose. According to the CDC, use of tecovirimat should be limited to individuals at high risk of disease.
The NIH is currently developing a U.S.-based randomized controlled trial (RCT) to confirm whether tecovirimat effectively treats mpox in humans. These trials will be used to determine whether the FDA will approve it for mpox.
Can you make a full recovery? Are there lasting effects?
While most people recover from mpox within a few weeks, some long-term complications can occur. These include new skin infections, pneumonia, confusion, and eye problems.
If you had mpox before, can you get it again?
It is not known whether a previous mpox infection gives you immunity against future infections and if so, for how long. For that reason, if you have had mpox in the past, you should be doing everything you can to avoid getting re-infected.