Faced with a limited supply of the monkeypox vaccine, FDA has authorized an alternative injection method that gives patients one-fifth of the current dose—but research is limited on the method, causing some debate among experts.

Demand for monkeypox vaccines is 'overwhelming' amid limited supply

FDA authorizes intradermal monkeypox vaccines

Last week, the Biden administration declared monkeypox a public health emergency, giving the administration more flexibility in responding to the outbreak—a move that many public health experts said was long overdue.

The public health emergency declaration gives the government flexibility in responding to the outbreak and the stigma around the disease among men who have sex with men (MSM), according to Demetre Daskalakis, deputy coordinator of the White House's new national monkeypox response team.

FDA Commissioner Robert Califf also announced that the United States ordered additional doses of the Jynneos vaccine, which is used to prevent monkeypox, and was considering adjusting how the vaccine is administered.

According to Califf, if the vaccine is injected intradermally (into the skin) rather than the current subcutaneous method (into underlying fat), the same dosage of the vaccine could yield as many as five times the number of doses.

On Tuesday, FDA issued an emergency use authorization for the Jyennos monkeypox vaccine to allow intradermal injection for people ages 18 and older at high risk for infection.

"The FDA quickly explored other scientifically appropriate options to facilitate access to the vaccine for all impacted individuals. By increasing the number of available doses, more individuals who want to be vaccinated against monkeypox will now have the opportunity to do so," Califf said in a statement.

While the administration has already invested over $1 billion developing Jynneos, it only has 1.1 million shots. According to the Times, the government needs around three times as many doses to protect the 1.6 million to 1.7 million Americans CDC says face a high risk of contracting the virus.

The debate over intradermal injection of the monkeypox vaccine

Research on intradermal injection of the monkeypox vaccine largely comes from a single study. According to the study, intradermal injection produces a strong immune response that is comparable to the response from a regular dose injected into an individual's underlying fat.

According to John Beigel, an NIH associate director of clinical research who has briefed federal health officials and the World Health Organization, switching to the intradermal method is a better way to preserve the monkeypox vaccine than only administering one of the two doses, as some jurisdictions, such as New York, are currently doing. A single dose does not provide nearly as strong an immune response as two doses, he noted.

"The upside is you can stretch out doses," said John P. Moore, a virologist at Weill Cornell Medicine. "The downside is, if you cut it too far or take too many liberties, you reduce the efficacy. And how are you going to know that? It's educated guesswork."

In addition, some experts have noted that the intradermal method can be difficult for those administering vaccines. They must guide a needle into a thin space—and a patient may not receive a large enough dose of the vaccine if a vaccinator accidentally inserts the needle into underlying fat. However, if they do not insert the needle far enough, some of the vaccine could leak out.

While evidence suggests that intradermal shots typically cause more redness and swelling, it also suggests they are less painful than a normal injection. The method has been applied in other situations, including polio vaccination campaigns, for rabies, and tuberculosis skin tests.

Previously, NIH planned additional studies into how well intradermal shots work with the monkeypox vaccine, but the results are not expected to be released until later this year. Ultimately, top federal officials over the weekend decided that the government needed to move to adopt the approach. (LaFraniere/Weiland, New York Times, 8/8; Branswell, STAT+, 7/15; Chen, Axios, 8/9)