The Centers for Disease Control and Prevention is sending out a warning to people with advanced HIV that they’re at a higher risk of severe illness if they get infected with monkeypox.

The virus was declared a national public health emergency on Thursday. Monkeypox cases topped 1,700 on Friday in New York City, making up just under a quarter of all the cases nationwide. The city's Health Department opened up 23,000 vaccination appointments Thursday at 6 p.m. Within hours, all those openings were booked.

The federal government is set to send thousands of vaccine doses by the beginning of September.

The CDC says 99% of cases across the country have been in men - 94% reported recently getting intimate with another man.

Doctors are cautioning that monkeypox can be spread through exposure to contaminated clothing or bedding or very close face-to-face contact. They added that some patients aren't experiencing those initial flu-like symptoms, instead just developing that rash that looks like blisters or pimples.

Monkeypox can take up to four weeks to recover, while developing symptoms can form three weeks after exposure.