Officials are grappling with whether to allow the new monkeypox vaccination strategy

WASHINGTON — It sounded like a simple solution to the monkeypox vaccine shortage: By simply changing how doses are given, the federal government could vaccinate five times as many people with the stockpile it has on hand.

But the approach — injecting one-fifth of the current dose into the skin instead of a full dose into the underlying fat — isn’t actually that simple, experts say. And some federal officials worry about changing the method without more research, even though Dr. Robert M. Califf, head of the Food and Drug Administration, described the proposal Thursday as promising.

Some outside experts, too, are calling for caution. “From a basic science perspective, this should work,” said Dr. Jay K. Varma, director of the Cornell Center for Pandemic Prevention and Response. “But, of course, there are many things in life, in science, that we think should work, and when we actually do them, they don’t.”

Expanding doses of the vaccine, Jynneos, could help the federal government resolve a predicament it partly created. Despite investing more than $1 billion to develop the two-dose vaccine for use against both smallpox and smallpox, the government has only 1.1 million shots on hand, in part because it was slow to order bulk vaccine stocks to be processed in vials.

That supply is enough to cover 550,000 people, but about three times as many doses are needed to cover the 1.6 to 1.7 million Americans who, according to the Centers for Disease Control and Prevention, are at high risk of monkeypox. Currently, the virus is spread primarily through skin-to-skin contact during sex between gay and bisexual men, the CDC said.

Some federal officials hope that by injecting a smaller dose of the vaccine between the layers of the skin, called an intradermal shot, the Biden administration could contain the outbreak before it spreads more widely.

However, some experts argue that this approach has not been sufficiently studied. They also warn that some vaccinators will need training to get the shots right, which could slow vaccination efforts. Otherwise, the government could end up wasting doses, not saving them.

Intradermal injection involves carefully guiding a needle into the layers of the skin, a thin space with immune cells. If a vaccinator goes too deep and injects the dose into the fat, the patient may not get enough vaccine, experts say. But if the needle is not inserted far enough, some of the vaccine could leak back out.

“If you give a lower dose and you don’t inject it into the skin correctly — you might inject it in the wrong place — you might not get a protective vaccine,” said Dr. Phil Krause, who retired as a senior FDA vaccine regulator last year and worked for the licensing of Jynneos by the organization. “If you ask for this to be done nationally in millions of doses, it’s much easier to make mistakes in the administration of the vaccine.”

On the other hand, the method has a history. It has been used in polio vaccination campaigns when doses have been limited, as well as for rabies and tuberculosis skin tests.

“It’s not a brand new idea,” said Dr. Anthony S. Fauci, President Biden’s chief medical adviser. “We were thinking of this as a vaccine shortage strategy years ago.”

Vaccinators have used special bifurcated needles in smallpox vaccination campaigns that have allowed them to give intradermal injections more evenly and cheaply.

Dr. John Beigel, associate director of clinical research at the National Institutes of Health, said a government-sponsored study of Jynneos published in 2015; compared the intradermal approach with the standard injection method and found that it elicited a comparable level of neutralizing antibodies, a measure of the strength of the immune response. The intradermal method caused more redness, swelling and itching, but the standard injection was more painful.

Dr. Beigel said switching to the intradermal method was a better option for preserving the vaccine than giving just one shot, as some jurisdictions do now, because research has shown that one shot doesn’t elicit nearly as strong an immune response.

“One dose is not likely to be effective,” he said, adding that the intradermal method “is an acceptable way.”

Although the 2015 trial included hundreds of participants, some experts note that it was a single study that was limited in what it measured. Researchers at NIH planned to test the intradermal strategy for Jynneos a trial which was due to start in a few weeks. But results weren’t expected until late fall or early winter, and that plan is currently up in the air.

Dr. H. Clifford Lane, the clinical director of the National Institute of Allergy and Infectious Diseases of Dr. Fauci at the NIH said that while researchers could glean information by following people who get vaccinated, a traditional clinical trial would provide a clearer picture.

“I can understand doing it as long as it’s very clear why it’s being done,” he said of the intradermal strategy. “The question is: How can we expand current supplies without significantly compromising efficiency?”

Another question is how well the vaccine will actually work: It was licensed in 2019 for use against both smallpox and smallpox after studies showed it elicited a stronger immune response than an older vaccine. The drug itself was approved because it compared favorably to an even older vaccine, federal officials said.

Monkeypox is rarely fatal and no deaths have been reported in the United States. Symptoms usually subside within two to four weeks. But with the outbreak growing from eight reported cases in late May to 7,510 nowthe administration tries to improve the vaccination rate and the availability of tests and treatments.

For now, the outbreak is almost entirely confined to men who have sex with men, with those who have multiple partners considered particularly at risk. However, five cases involving children have been reported so far.On Friday, the Illinois Department of Public Health announced that an adult who worked at a day care center tested positive for monkeypox and that the children and other staff members there were being tested. .

The public health emergency declaration on Thursday allowed the federal government to speed up monkeypox investigations and approve grants, but did not invoke the FDA’s emergency powers. Changing the injection mode would require a second type of emergency statementgiving the Food and Drug Administration more leeway to issue emergency use permits.

Federal regulators can issue emergency product licenses when they believe the potential benefits outweigh the potential risks. Early in the coronavirus pandemic, the Trump administration issued the same type of emergency declaration, allowing the FDA to make Covid-19 vaccines available to Americans many months before regulators issued full approvals.

Dr. Khalif, the FDA commissioner, said Thursday that regulators would continue to ensure that the vaccine was delivered in a safe and effective manner. He said regulators would likely decide in the coming days whether to pursue the intradermal strategy, but that it “looks good right now” — a comment that some outside experts said appeared to preempt the career regulators’ discussions.

Emily Cochrane and Tracey Tully contributed reporting.