(Adds quotes, case data and background)
By Ahmed Aboulenein and Kanishka Singh
WASHINGTON, Aug 18 (Reuters) - The United States said on Thursday it will boost its supply of monkeypox vaccine by making available an extra 1.8 million doses of Bavarian Nordic's Jynneos shot, as the number of reported cases in the country rose above 13,500.
Rochelle Walensky, director of the Centers for Disease Control and Prevention (CDC), gave the figure for reported cases as of Aug.17, which represent more than a third of the global total of 39,000, at a White House briefing.
"It's critical that we do all we can to keep this dangerous virus from spreading," Secretary of Health and Human Services Xavier Becerra said at the briefing.
The Department of Health and Human Services (HHS) is making 360,000 vaccine vials available to order from next week, said Assistant Secretary for Preparedness and Response Dawn O'Connell, which is the equivalent of 1.8 million doses.
The U.S. Food and Drug Administration (FDA) last week authorized administering Bavarian Nordic's Jynneos shot intradermally, between the layers of the skin, increasing by fivefold the doses that can be used from a vial.
Bavarian Nordic has raised doubts about the safety of the method, citing a lack of data and evidence that injecting Jynneos in this way could result in increased reactions compared to injecting it underneath the skin.
The additional doses would be available for states and local health departments that administer the vaccine intradermally, and have used 90% of their current supply, White House monkeypox response coordinator Bob Fenton said.
The U.S. is also making 50,000 courses of SIGA Technologies Inc's TPOXX antiviral treatment available for people who test positive, said Fenton. State and local health departments can start ordering them next week.
In addition, President Joe Biden's administration is setting aside vaccine doses for areas hosting large gatherings of high-risk groups, he said, which state and local health departments can order on top of their existing allocations and supply.
"HHS is launching a pilot program that will provide up to 50,000 doses from the National Stockpile to be made available for pride and other events that will have high attendance of gay and bisexual men," Fenton added.
Around 98% of monkeypox cases nationwide occurred among those assigned the male sex at birth, Walensky said.
Among cases with known recent sexual history and gender, 93% were among men who reported recent sexual contact with other men, down from 99% in late July.
The pattern of sexual transmission in men is not typical. In Africa, where monkeypox has been circulating since the 1970s, 60% of cases are in men, and 40% occur in women.
Of the more than 6,000 U.S. cases for which race and ethnicity data is available, about 35% occurred among white, non-Hispanic people, Walensky said, adding that another 28% were in Black people and 33% in Hispanic people.
The median age of cases is 35, she added.
(Reporting by Ahmed Aboulenein and Kanishka Singh; Editing by Mark Porter, Frances Kerry and Alexander Smith)