Deadly mpox outbreak abroad is a 'global threat,' CDC warns. Here's what to know.

A gloved hand draws a vaccine into a syringe.
The CDC is urging at-risk Americans to get vaccinated against mpox as a deadlier strain in the Democratic Republic of the Congo poses a “global threat.” (Jeenah Moon/AP)

The Centers for Disease Control and Prevention is warning Americans about a deadlier form of mpox that’s spreading rapidly through the Democratic Republic of the Congo (DRC), saying it “poses a global threat.” Monkeypox cases in the U.S. have declined since their peak in August 2022, but health officials are urging caution. So far, no cases of this deadlier strain have been detected in the U.S., but the CDC is ramping up surveillance for mpox and advising people at high risk of infection to get vaccinated and take precautions.

Here’s what experts want you to know about the resurgence of mpox.

Mpox is an infectious disease caused by the monkeypox virus. It typically causes a rash and flu-like symptoms, including body aches, fever, chills, headache and fatigue, though it can be fatal, particularly for people with compromised immune systems.

In the spring of 2022, mpox began spreading in the U.S., mainly among gay, bisexual and other men who have sex with men. The virus is transmitted through “prolonged intimate contact with someone who has active lesions,” which are the red, sometimes painful sores that make up an mpox rash, Dr. Boghuma Titanji, a professor of infectious diseases at Emory University School of Medicine, tells Yahoo Life. “When you’re talking about close intimate contact, that includes sex, because when people have sex, they are close together,” but mpox is not a sexually transmitted infection and can be spread without sexual contact, she says.

The deadlier of two forms of the mpox virus — known as clade I — has driven cases in the DRC to a record high. Nearly 20,000 suspected mpox cases were diagnosed there between January 1, 2023, and April 14, 2024, according to a recent CDC report. Almost 1,000 people died of the infection and more than two-thirds of those were children.

Clade I has a considerably higher mortality rate than clade II, which hit the U.S. in 2022, killing up to 10% of the people who contract it, compared to 3.6% or less of those infected with the milder form of mpox (though, Titanji notes, this may be in part because there is less access to treatment in the areas of Africa hit hardest by clade I).

For now, the deadlier clade is chiefly affecting countries in Central Africa, including the DRC and Cameroon, Titanji says. None of the 343 samples taken from people with mpox in the U.S. that the CDC tested between Dec. 1, 2023, and April 14, 2024, belonged to clade I.

But, in 2022, the less deadly form of mpox (clade II) quickly went from a regional concern to a global one, as travel helped spread the infection to 110 countries, including much of Europe and the U.S., ultimately infecting more than 32,000 Americans. The CDC is concerned that international spread could happen again with clade I. And the mpox tests most commonly used in the U.S. don’t distinguish between the two subtypes of the virus, making it hard to know whether clade I has arrived, Dr. Amesh Adalja, an infectious disease professor at the Johns Hopkins Center for Health Security, tells Yahoo Life.

The CDC’s main goal, for now, is to monitor for travelers coming from the DRC who might have mpox and to raise awareness, especially among those at high risk of infection. “The U.S. has never gone down to zero cases” since the outbreak began two years ago, Titanji says. “We still have, on average, 200 cases being reported every month,” and fewer than 1 in 4 at-risk people has gotten their full series of vaccinations against the virus, meaning most are still vulnerable to infection.

As the outbreak continues, men who have sex with men are still at highest risk of infection. “We saw a disproportionate impact among interconnected social and sexual networks” during the 2022 surge, says Titanji. “It was really able to spread in a niche group.” But, she adds: “We [also] saw infections among all sex types and preferences. It’s an infectious disease; it can infect anyone if you have exposure.” In the DRC, there has been considerable spread between heterosexual partners, and spread among children who may live or play in close quarters, she explains.

In the U.S., anyone eligible for vaccination against mpox — including gay and bisexual men — who hasn’t gotten both doses of the shot should do so, advise Titanji and Adalja. That’s especially important for those who are living with HIV or other immunocompromising conditions, because mpox is especially dangerous to these people, CDC data suggests.

Summer, with its densely packed social activities and uptick in travel, also brings additional risks for mpox transmission, Titanji notes. Plus, “it’s Pride month, so there are lots of festivals that get people intermingling and coming together,” she says. “This creates opportunities for transmission to occur, and a flare-up of an outbreak to happen.”

Titanji advises that people monitor themselves for lesions and flu-like symptoms and consider getting tested for mpox before engaging in close contact with others. She also recommends using condoms to reduce the likelihood of contact with lesions. But, she adds, it doesn’t mean you have to put fun on hold. Instead, “utilize the tools that we have in the public health space that allow people to be able to still enjoy the summer, and enjoy having sex with their partners, but [do] it in a way that doesn’t increase their risk of exposure to an infection like mpox,” Titanji says.