Mpox is in the same class of viruses as smallpox, which had similar but more severe symptoms before its eradication in the late 1970s.

The mpox virus is primarily spread through close human-to-human contact, including in the respiratory droplets and contact with skin lesions of someone who has the disease. The virus can enter a person’s body through broken skin, the respiratory tract, and the eyes, nose, mouth, or through sexual contact. In order for the virus to spread through respiratory droplets, a person has to be face-to-face with someone who is sick for a prolonged period—putting health workers and family members at the greatest risk of contracting the virus from someone who has it. It can also be spread by touching objects like clothes or furniture that have the virus on them.

The current outbreak has disproportionately affected men who have sex with men, but anyone can become infected if exposed to the virus.

While the most common symptoms of mpox are skin lesions, fever, headache, muscle aches, exhaustion, and swollen lymph nodes, complications have been reported, primarily among people with other health conditions. These include secondary infections, bronchopneumonia, sepsis, encephalitis and infection of the cornea and subsequent loss of vision.

Most people who are infected with mpox recover from their symptoms within four weeks. The percentage of people who die from mpox compared to the number of those infected has historically been 3-6 percent in places where the disease is endemic.

The severity of one’s illness is also dependent on which strain of the virus they contract. There are two main strains of mpox, the Clade I and Clade II strains. The Clade II strain of mpox causes less severe disease compared to the Clade I strain of the disease, with case fatality rates of 3.6 percent and 10.6 percent, respectively.

The most effective test for mpox is a real-time polymerase chain reaction (RT-PCR) test that takes a sample from a person’s infected skin lesion. There are currently no over-the-counter diagnostic tests available.

Two antiviral medicines—tecovirimat and brincidofovir—were recently approved for poxviruses, including smallpox and mpox, in the US and/or Europe.  

Prevention is also key in curbing the spread of mpox. People should avoid close contact with those who have mpox or an mpox-like rash, avoid touching objects that have been used by people with the virus, and wash their hands often.

Data from studies conducted in Africa show that the smallpox vaccine may be up to 85 percent effective in preventing mpox infection. However, since smallpox was eradicated and vaccine campaigns against it have ended, fewer people across the world have existing immunity.

Currently, more than 116 million doses of smallpox vaccine are scattered among various national stockpiles as part of biodefence strategies against smallpox, with the US holding the vast majority. The US is currently stockpiling more than 100 million doses of a smallpox vaccine called ACAM2000. However, this vaccine can cause significant side effects and adverse events. The preferred vaccine to protect against mpox is JYNNEOS, but supply of this vaccine is much more limited, especially in countries where mpox is endemic.

In order to protect people who are most at risk of contracting mpox, it is critical that vaccines are widely accessible and affordable and that wealthy countries do not hoard them as has been seen during the COVID-19 pandemic. It is especially important to ensure access to vaccines for people living in the places that have historically seen the most mpox cases, including countries in West and Central Africa.