The head of the World Health Organization, Tedros Adhanom Ghebreyesus, declared Saturday the monkeypox outbreak to be a global health emergency - the highest alarm it can sound.

"I have decided that the global monkeypox outbreak represents a public health emergency of international concern," Tedros announced.

Monkeypox has affected over 15,800 people in 72 countries, according to a tally by the US Centers for Disease Control and Prevention (CDC) published on July 20.

A surge in monkeypox infections has been reported since early May outside the West and Central African countries where the disease has long been endemic.

On June 23, the WHO convened an emergency committee (EC) of experts to decide if monkeypox constitutes a so-called Public Health Emergency of International Concern (PHEIC) -- the UN health agency's highest alert level. 

But a majority advised Tedros that the situation, at that point, had not met the threshold.

The second meeting was called on Thursday with case numbers rising further, where Tedros said he was worried.

"I need your advice in assessing the immediate and mid-term public health implications," Tedros told the meeting, which lasted for more than six hours.

"Grave consequences for global health"

A US health expert sounded a grim warning late Friday.

"Since the last monkeypox EC just weeks ago we've seen an exponential rise in cases. It’s inevitable that cases will dramatically rise in the coming weeks & months. That’s why Tedros must sound the global alarm," Lawrence Gostin, the director of the WHO Collaborating Center on National and Global Health Law, stressed on Twitter.

"A failure to act will have grave consequences for global health," he warned.

Monkeypox less dangerous & contagious than smallpox

A viral infection resembling smallpox and first detected in humans in 1970, monkeypox is less dangerous and contagious than smallpox, which was eradicated in 1980.

95% of cases have been transmitted through sexual activity, according to a study of 528 people in 16 countries published in the New England Journal of Medicine - the largest research to date.

The European Union's drug watchdog on Friday recommended the approval of Imvanex, a smallpox vaccine, to treat monkeypox.

Imvanex, developed by Danish drugmaker Bavarian Nordic, has been approved in the EU since 2013 for the prevention of smallpox. 

It was also considered a potential vaccine for monkeypox because of the similarity between the monkeypox virus and the smallpox virus.  

The first symptoms of monkeypox are fever, headaches, muscle pain, and back pain during the course of five days. 

Rashes subsequently appear on the face, palms of hands, and soles of feet, followed by lesions, spots, and finally scabs.