The World Health Organization on Saturday declared the growing monkeypox outbreak to be “a public health emergency of international concern.”

During a briefing in Geneva on Saturday, WHO Director-General Dr. Tedros Adhanom Ghebreyesus said, “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.”

According to Ghebreyesus, more than 16,000 cases of monkeypox have been reported across 75 countries, with five deaths confirmed in Africa. As reported by CNBC, Dr. Rosamund Lewis—known for her work as WHO’s leading monkeypox expert—shared that 99 percent of all the monkeypox cases outside of Africa were in men and that of those, 98 percent involved men who have sex with men. 

“WHO’s assessment is that the risk of monkeypox is moderate globally and in all regions, except in the European region where we assess the risk as high,” Ghebreyesus said. “There is also a clear risk of further international spread, although the risk of interference with international traffic remains low for the moment.”

He added, “So in short, 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.”

The announcement arrives just a day after the CDC announced the first two U.S. cases of monkeypox in children. “We became aware of these cases just this week, and we’ve been working with the jurisdictions to understand more about these cases,” the CDC’s Jennifer McQuiston told reporters on Friday, per CBS News.

This is the seventh time since 2007 WHO has declared a Public Health Emergency of International Concern.

As for monkeypox, specifically, the disease itself caused by the monkeypox virus and can exhibit as a rash that—according to the CDC—may resemble “pimples or blisters” which are also sometimes accompanied with flu-like symptoms. Spread is said to be made possible “to anyone” via close, personal contact, including potentially touching objects or other surfaces that were previously used by someone with monkeypox or via direct contact with “rash, scabs, or body fluids.” Respiratory secretions can also cause spread.

Symptoms have been determined to typically manifest within three weeks of exposure. As of June of this year, two vaccines were licensed by the FDA for monkeypox prevention. The European Medicines Agency, meanwhile, was reported last week by the Associated Press to have urged the authorization of a Bavarian Nordic smallpox vaccine for use in the fight against monkeypox infections.