“We have an outbreak that has spread around the world rapidly, through new modes of transmission, about which we understand too little, and which meets the criteria in the international health regulations,” WHO Director General Dr. Tedros Adhanom Ghebreyesus said at an afternoon press conference announcing the decision.

“For all of these reasons, I have decided that the global monkeypox outbreak represents a public health emergency of international concern.”

The committee, when convened Thursday, did not reach a decision on the matter—this roughly a month after its first meeting, at which it also failed to reach a consensus.

In the meantime the outbreak grew from more than 3,000 cases in 47 countries to more than 16,000 cases in 75 countries and territories as of this week, with five deaths, Adhanom Ghebreyesus said.

Given international health regulations, however—which required him to consider the rapidity of the spread of the virus and the potential to interfere with international travel, among other factors—the head of the international health organization went ahead with the declaration, acting as a tie-breaker in the setting of a simple majority.

Nine members of the committee voted for the declaration of an international health emergency and six against, he said. Last time, three voted for and 11 against.

The risk of monkeypox to the global community is currently moderate, with the exception of Europe, where the majority of cases have occurred since May and where risk is high, Adhanom Ghebreyesus said.

Nearly all cases of monkeypox continue to occur among men who have sex with men, WHO officials said Saturday, but the risk of spill-over into other populations persists, with several cases already reported in children who live with someone who contracted the disease.

Before Saturday, WHO emergency committees only existed for COVID-19 and polio. Seven additional past emergency committees have previously been convened for diseases including Ebola, H1N1, and MERS.

A growing outbreak with atypical spread

Monkeypox is usually found in rural African areas where people have close contact with infected rats and squirrels. Recent cases, however, have occurred in countries where the virus has not previously been seen, and in individuals without a travel history, indicating that it likely has been circulating unnoticed for some time.

When the virus is transmitted human to human, it’s typically through close contact, which may include sex and could include contact with personal items like sheets and clothing. While it’s not considered a sexually transmitted infection, public health officials say many recent cases have been found among men who have sex with men, and note that it’s difficult to tease out sexual transmission from close-contact transmission. Airborne transmission is known to be possible but has yet to be confirmed.

With smallpox declared eradicated by the WHO in 1980 and the vaccine for it, which works on monkeypox, no longer widely administered, the population has a low level of immunity against poxviruses, WHO officials have said. That means transmission into the wider population could occur.

Symptoms are similar to but milder than those of smallpox, according to the CDC. Initial symptoms usually include fever, headache, muscle aches, and exhaustion. Within one to three days, patients develop a rash, usually starting on the face and then spreading to other parts of the body. Lesions progress through various stages before scabbing. The illness usually lasts two to four weeks. The typical incubation period is seven to 14 days but can range from five to 21 days.

But symptoms in new cases appear to differ from those of classic cases—at least in some instances—with recent reports of lesions more subtle than usual and some cases involving just one lesion, health officials have said.