U.S. health regulators have authorized injecting a monkeypox vaccine intradermally in adults, meaning between layers of the skin rather than below the skin, in an effort to stretch out low vaccine supplies, the U.S. Food and Drug Administration (FDA) announced on Tuesday.

The emergency use authorization for Bavarian Nordic's Jynneos monkeypox vaccine will increase available doses fivefold as it only uses a fraction of the dose but provides the same protection, health officials said at a White House briefing.

The FDA authorization comes after the United States and the World Health Organization declared monkeypox a public health emergency to bolster the response against the outbreak.

Jynneos was approved in 2019 for smallpox and monkeypox prevention in high risk adults 18 years of age and older. Under its original approval it was to be administered beneath the skin, or subcutaneously, as two doses.

Two doses of the vaccine given four weeks apart will still be needed with the intradermal method, the agency said.

The FDA approval also allows people under 18 years to receive the vaccine by subcutaneous injection if they are determined to be at high risk of monkeypox infection. The FDA is staying with this method for children as it is easier to administer and there is not as much data available.

The United States tripled its monkeypox cases in just 15 days after the Centers for Disease Control and Prevention (CDC) recorded 1,424 additional cases on Monday, the highest daily count since the outbreak in the country in May.

As of Monday, the United States had the world's highest number of confirmed monkeypox cases , which stood at 8,934. It is likely that the figure is a undercount due to the lack of testing.

The number of confirmed cases in the United States is almost 30 percent of the global total of over 30,189 so far, even though the country has less than 5 percent of the world's population.

(With input from agencies)

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