Monkeypox vaccines: Why does the U.S. government want 5 people to share 1 dose?

Could less equal more?

US Food and Drug Administration officials on Thursday announced their consideration of a plan to expand the nation’s monkeypox vaccine supply by splitting doses.

The announcement came just moments after Department of Health and Human Services Secretary Xavier Becerra declared a public health emergency over the globally circulating virus, once endemic only to Africa.

On a Thursday press call, FDA Commissioner Dr. Robert Califf said the agency is considering a process called “dose sparing” to stretch its supply. It would allow health care providers to split a one-dose vial of Jynneos—one of two smallpox vaccines approved for fellow poxvirus monkeypox, and the safest by far—into five doses, to be administered to five patients.

The doses would be administered intradermally, or between layers of skin, instead of subcutaneously, or under the skin. The approach provides improved immune response and does not jeopardize safety or effectiveness, Califf said.

The agency will likely make a decision on dose sparing “within the next few days,” Califf said Thursday, adding that the odds it would proceed with the plan were “looking good.” Although the vaccine is FDA approved, an emergency use authorization would be needed due to changes in dosing and administration.

‘Safe and efficient mass vaccination’

While “dose sparing” might sound like a desperate solution to inadequate vaccine supply, it’s “not being done randomly.” There’s data behind the concept, Dr. Lindsey Baden, an infectious disease specialist at Brigham and Women’s Hospital in Massachusetts and a Harvard Medical School professor, told Fortune.

A prior study of dose sparing involving smallpox vaccine showed that a fifth of a dose—and perhaps even a tenth—produced an immune response comparable to a whole dose, Baden said.

Administering a small dose of smallpox vaccine intradermally allows for “safe and efficient mass vaccination, a prerequisite when vaccination of a large population at a short time is needed,” the authors of a 2018 study published in the journal Vaccines reported.

The approach is “definitely worth exploring,” Dr. Alexandra Brugler Yonts, an infectious disease specialist at Children’s National Hospital in Washington, DC, who assisted in the FDA’s review of Jynneos, told Fortune.

But “there isn’t much available data specifically for Jynneos,” she cautioned.

“Any studies on this route of delivery were not evaluated as part of the initial licensing of Jynneos in 2019, which is why intradermal injection is not included on the current package insert,” she said. “But if the FDA has that data now to review and find it convincing, it would be a reasonable temporizing measure.”

She is concerned that smaller doses may not be adequate for those with HIV or those who are immunocompromised.

“Some protection is better than none, but the people being vaccinated should be warned and advised to continue other protective measures to minimize physical or intense close contact with potentially infected individuals,” she said.

“Just like with COVID, receiving the vaccination—especially only a single dose or smaller doses—is not a free pass to blindly take part in high risk behavior in the context of an active outbreak.”

Baden is concerned with the safety and efficacy of every treatment—a dose-sparing approach to Jynneos included—and thinks more data is always better.

“We can always want more science,” he said. “But more doesn’t mean you haven’t already demonstrated the point.”