A proposal to stretch the US monkeypox vaccine supply by injecting smaller doses more superficially has promise because of the technology used to make the shot, infectious disease specialists say.
The head of the Food and Drug Administration said the agency is exploring a strategy that involves injecting a smaller dose of vaccine intradermally, or in the upper layer of the skin. The strategy, called dose sparing, could turn a one-dose vial of the vaccine into up to five separate doses.
FDA Commissioner Robert M. Califf said he expects a final decision to happen within the next few days.
“We’re feeling very good about the intradermal approach,” Califf said during a press briefing Thursday shortly after Health and Human Services Secretary Xavier Becerra announced he’s declaring a public health emergency for monkeypox. “It really means basically sticking the needle within the skin and creating a little pocket there into which the vaccine goes. This is really nothing highly unusual. It’s done in other situations routinely.”
But the approach may not work for all vaccines, such as protein-based vaccines.
Some 600,000 doses have been delivered to states, Becerra said. But Rochelle Walensky, director of the Centers for Disease Control and Prevention, estimated there are about 1.6 million to 1.7 million people who are at highest risk for monkeypox right now.
“Stretching the vaccine supply as much as possible is the best way to increase the immunity level in the at-risk community,” Amesh A. Adalja, senior scholar at the Johns Hopkins Center for Health Security, said in an email.
The US used the dose sparing approach during the 2004 to 2005 flu season, when potential contamination cut the vaccine supply in half. A New England Journal of Medicine study found that approach elicited the same or better immune response.
Health-care workers also used the intradermal approach for smallpox “in the old days,” Lee Riley, chair of the University of California, Berkeley’s Division of Infectious Disease and Vaccinology, said.
“They used what’s called a kind of a bifurcated needle, where they dip this needle into kind of the solution of the vaccine, and then they kind of prick a skin with it, and then allow the vaccine to get underneath the skin layer.”
An intradermal injection can work because Jynneos is an attenuated vaccine, which means the company used a weakened form of the virus to develop the vaccine, Riley said.
“Whenever you have a attenuated virus, it doesn’t replicate in human cells. And so in certain parts of the skin, it works better,” Riley said. This approach wouldn’t work for a protein-based vaccine that uses harmless proteins from the virus to stimulate the immune system.
With a protein-based based vaccine, “you have to put into the muscle so that it’s distributed by the blood and then get recognized by the immune cells,” Riley said. “You can’t do this with every type of vaccine, It really depends on the type of vaccine formulation.”
Sometimes an intradermal injection is more difficult than an intramuscular or subcutaneous injection, Adalja said. " It may need special needles and training but [intradermal] is known to be a more immunogenic route of vaccination.”
Califf stressed that any new approaches in administering the monkeypox shot won’t affect the safety and efficacy profile of the vaccine. “Our ability to continue allowing safe, high-quality products or communities nationwide has and will always be top of mind,” he said.
With Jynneos, “it has scientific basis for doing this,” Riley said. “But the obvious thing is to just really ramp up the production of the vaccine.”