The U.S. is underreacting to the monkeypox outbreak. Given that a vaccine is available for the infection—and can be targeted toward the people most at risk—public-health authorities and health-care providers need to move more quickly and forcefully to change the outbreak’s trajectory.

Monkeypox is related to smallpox, the only human virus that has been eradicated worldwide. A highly effective smallpox vaccine, called Jynneos, has been licensed in the United States for use against monkeypox as well. Data from Africa suggest that it is at least 85 percent effective in preventing the latter condition.

On June 1, the CDC updated its recommendations to say that Jynneos is the preferred post-exposure prophylaxis for health-care workers and others who have had close contact with monkeypox patients. The U.S. has about 36,000 doses in its stockpile and expects 300,000 additional doses in coming weeks. It needs to purchase many more—and should offer the vaccine to all MSM at risk of exposure in the next month. Canada just signed a $56 million deal with the manufacturer of the Jynneos vaccine, and Quebec has started offering the vaccine to all MSM. The U.K. is expanding its vaccination campaign as of this week to offer shots to the gay and bisexual men at highest risk of exposure. The New York City Health Department announced the opening yesterday of a clinic in Chelsea that will offer the vaccine to MSM who have had multiple partners in the past 14 days.