The monkeypox vaccine is now available at 11 sites around Massachusetts, state public health officials said Monday.

There had been more than 1,800 cases of monkeypox reported in the U.S. as of Friday, according to the Centers for Disease Control and Prevention, 51 of which were in Massachusetts. New York, California and Illinois had the most cases.

Nearly all are in men and the vast majority had same-sex encounters, according to the CDC.

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The vaccine, when properly administered before or soon after exposure, can help protect against illness, the state Department of Public Health said. The Jynneos vaccine available in Massachusetts, requires two shots, 28 days apart for maximum effectiveness. People are considered fully vaccinated about two weeks after their second shot.

Monkeypox vaccine vials

Massachusetts is opening monkeypox vaccine sites in 11 locations. (REUTERS/Dado Ruvic/Illustration/File Photo)

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The virus mainly spreads through skin-on-skin contact, but it can also transmit through touching linens used by someone with monkeypox.

People with monkeypox may experience fever, body aches, chills and fatigue. Many in the outbreak have developed bumps on their body.

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The vaccine, available to people who live or work in Massachusetts who also meet the CDC’s eligibility criteria, is being administered at three sites in Boston, two in Springfield, as well as in Provincetown, Randolph, Lawrence, Framingham, Worcester and New Bedford.