Officials Wrestle With Whether to Allow New Monkeypox Vaccination Strategy

WASHINGTON — It sounded like a simple solution to the shortage of monkeypox vaccine: Merely by changing the way doses are injected, the federal government could vaccinate five times as many people with the supply it has in hand.

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

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

Stretching out doses of the vaccine, Jynneos, could help the federal government resolve a predicament partly of its own making. Even though it invested more than $1 billion developing the two-dose vaccine to use against both monkeypox and smallpox, the government only has 1.1 million shots on hand, partly because it was slow to order bulk vaccine stocks to be processed into vials.

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

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

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

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

“If you’re giving a lower dose and you don’t inject it properly into the skin — you might inject it into the wrong place — you may not be giving a protective vaccine,” said Dr. Phil Krause, who retired as a senior F.D.A. vaccine regulator last year and worked on the agency’s licensing of Jynneos. “If you ask this to be done nationwide in millions of doses, it’s a lot easier for there to be mistakes made in the administration of the vaccine.”

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

“It’s not a brand-new concept,” said…