New York City is launching a monkeypox vaccine clinic for people who may have been exposed to the virus. 

With 28 people testing positive for the virus in the city since early May, the Big Apple now accounts for more than 20% of confirmed U.S. monkeypox cases. 

Monkeypox is a rare viral disease, similar to smallpox, that has mostly occurred in central and Western Africa, but new outbreaks have been reported around the globe this year. There were 3,308 confirmed cases in 42 countries as of June 22, with 155 cases reported in the U.S., according to the Centers for Disease Control and Prevention.

Monkeypox spreads when a person encounters the virus through close contact with another human, most often through direct contact with a rash or the sores of someone who has the virus, as well as through respiratory droplets that can be passed in prolonged close contact, including sex. It can also be spread through close contact with an animal infected with the virus, or items that could be contaminated with body fluids carrying the monkeypox virus, like bedding or clothing. 

And because the monkeypox virus belongs to the same family of viruses as smallpox, smallpox vaccines can protect people from getting monkeypox. The Jynneos vaccine made by Bavarian Nordic BVNKF, -3.82% has been licensed in the United States to prevent monkeypox and smallpox. And this two-dose vaccine is what will be administered in NYC’s new monkeypox vaccine site located at the Chelsea Sexual Health Clinic at 303 Ninth Ave., between West 27th and 28th streets, in Manhattan. The clinic is now open on Mondays, Tuesdays, Thursdays, Fridays and Sundays from 11 a.m. to 7 p.m. local time. You can make an appointment at nyc.gov/health/monkeypox.

People who may have had a recent exposure to monkeypox were already eligible for the vaccine in New York. The city health department has now expanded eligibility to “all gay, bisexual, and other men who have sex with men (cisgender or transgender) ages 18 and older who have had multiple or anonymous sex partners in the last 14 days.” This is because, while anyone can get and spread monkeypox, most of the cases in the current outbreak have been among gay, bisexual or other men who have sex with men, the health department explained. 

New York joins similar monkeypox vaccination efforts ramping up in Montreal and Toronto in Canada. The United Kingdom, which has the most reported monkeypox cases (793 as of June 22, per the CDC), recently widened eligibility for monkeypox vaccines by tens of thousands of people to stop the spread. 

Earlier in June, the U.S. government announced it had ordered 500,000 additional Jynneos doses to be delivered later this year. This would be added to the 72,000 Jynnous doses that the government already had on hand, as well as an earlier 300,000-dose order from vaccine maker Bavarian Nordic.

The original smallpox vaccine, ACAM2000, has also been shown to be about 85% effective in preventing monkeypox, although there were some serious side effects. So roughly half of all Americans have some immunity against monkeypox because they were vaccinated against smallpox, although smallpox vaccinations mostly ended in 1972, after the disease was eradicated in the country.

For more information about the monkeypox virus, including symptoms and travel advisories, check out MarketWatch’s monkeypox guide.