The World Health Organization has activated its highest alert level for the growing monkeypox outbreak, declaring the virus a public health emergency of international concern.

The rare designation means the WHO now views the outbreak as a significant enough threat to global health that a coordinated international response is needed to prevent the virus from spreading further and potentially escalating into a pandemic.

More than 16,000 cases of monkeypox have been reported across 75 countries so far this year, and the number of confirmed infections rose 77% from late June through early July, according to WHO data. Men who have sex with men are currently at highest risk of infection.