Facing a growing outbreak of the monkeypox virus, New York City health officials expanded access to a monkeypox vaccine on Thursday, offering it to a new group of people who may be at higher risk: men who have had multiple or anonymous male sexual partners over the last two weeks.

New York City is the first American jurisdiction to broaden access to the vaccine beyond close contacts of people infected, following similar moves in the United Kingdom and Canada.

Public health officials globally have been scrambling to craft an effective response to the outbreak, which has been spreading in dozens of countries since mid-May, particularly among networks of gay, bisexual and other men who have sex with men.