Mpox: What You Need to Know – Yale Medicine

[Originally published: July 11, 2022. Updated: Aug. 14, 2024.]

Mpox (formerly known as monkeypox), an infectious disease typically found in parts of Central and Western Africa, has again been labeled a global health emergency by the World Health Organization (WHO).

Mpox became a global concern in 2022 when a type of the virus spread to other countries. That outbreak led to more than 90,000 cases worldwide, including more than 32,000 in the United States.

In 2023, the WHO declared an end to the global health emergency based on a decline in new cases and steady progress in controlling the spread of the disease, even though it continued to circulate in the community.

Now, public health officials around the world are concerned about a new strain of the virus that has driven up the number of cases and deaths in the Democratic Republic of Congo and other African countries. No cases have been reported in U.S.

Although it can affect anyone, most mpox cases from the 2022 outbreak were sexually transmitted and reported in men who have sex with men (MSM). The 2022 outbreak was caused by a strain called Clade IIb. The current outbreak is caused by Clade I, a strain that can also be sexually transmitted, cause more severe illness, and lead to death in up to 10% of those infected.

For reasons not yet known, the virus, since 2022, is behaving in ways never before seen, with cases occurring in countries that dont normally see it. Before this, mpox was also not known to spread easily among people or to infect large groups at once. Now, it can spread through close contact.

We talked with Marwan Azar, MD, a Yale Medicine infectious diseases specialist about what we know so far about this new strain of mpox.

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Mpox: What You Need to Know - Yale Medicine