A vial of the Jynneos vaccine.Share on Pinterest
New federal guidelines may dramatically increase the number of people receiving the Jynneos monkeypox vaccine. Mario Tama/Getty Images
  • Federal officials issued an emergency use authorization (EUA) that would stretch the existing monkeypox vaccine supply.
  • The new approach involves injecting a small portion of the vaccine dose intradermally or in the skin, dramatically increasing the supply.
  • The vaccine is currently given subcutaneously or under the skin.

The U.S Food and Drug Administration has issued an emergency use authorization (EUA) for the current monkeypox vaccine that enables healthcare providers to stretch the current supply up to five-fold.

This change involves giving the Jynneos monkeypox vaccine intradermally or in the skin instead of subcutaneously or under the skin, using a fraction of a single-dose vial for each injection.

“In recent weeks the monkeypox virus has continued to spread at a rate that has made it clear our current vaccine supply will not meet the current demand,” FDA Commissioner Dr. Robert M. Califf said in a statement released today.

“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.”

Stretching out the doses could help the federal government protect more of the 1.7 million Americans the US Centers for Disease Control and Prevention (CDC) estimates are at high risk of monkeypox.

Currently, the federal government only has 1.1 million doses of Jynneos on hand, enough to deliver two standard doses to around 550,000 people.

Most routine vaccinations are given subcutaneously (injected underneath the skin) or intramuscularly (into the muscle).

The Jynneos monkeypox vaccine is currently approved by the FDA as two subcutaneous injections given 28 days apart.

With intradermal injection, a health care worker guides a needle between the layers of skin, an area rich in immune cells. If the needle goes too deep, not enough of the vaccine will reach those immune cells.

Intradermal injection is already used for the tuberculin skin test, also known as a PPD test.

Dr. Brandi Manning, an infectious diseases physician at The Ohio State University Wexner Medical Center in Columbus, said intradermal vaccination “theoretically” could be a very helpful strategy for protecting more people against monkeypox.

However, “we do not currently administer vaccines via this route very often in the United States,” she said, “so it may require some minor additional training for healthcare providers to learn this technique of vaccine administration.”

An intradermal strategy for this vaccine would also need to be tested in clinical trials.

Researchers at the US National Institutes of Health had been planning on testing this dose-sparing strategy in a clinical trial, although The New York Times reports that this plan is on hold for now.

In addition, before a switch to intradermal delivery of Jynneos could happen, the FDA would need to issue an emergency use authorization (EUA) allowing this injection method.

This is the same emergency power that the agency used to authorize the COVID-19 vaccines earlier in the pandemic.

While many vaccines — including the COVID-19 vaccines — are given using other injection methods, intradermal vaccination is not entirely new.

“It’s done in other situations routinely, so we’re confident about the administration of the dose,” Califf said.

Earlier studies found that this approach is effective for other types of vaccines, such as those that protect against influenza and rabies.

“Intradermal administration is safe and effective for some vaccines,” said Manning. In addition, studies looking at intradermal injection of other vaccines, such as influenza, “showed no difference in the immune response.”

Many of these studies also found that intradermal vaccination resulted in more local reactions such as redness, itching and swelling at the injection site, compared to subcutaneous or intramuscular injections.

However, systemic effects such as fever, headache and muscle pain were similar for all vaccination methods.

Other studies suggest that a dose-sparing approach might also work for subcutaneous and intramuscular vaccinations, although more research is needed on this strategy.