With demand for the monkeypox vaccine far outpacing supply, the United States is changing its vaccination strategy to expand availability.
The JYNNEOS vaccine, which is the only FDA-licensed monkeypox virus (MPV) vaccine in the country, can now be administered intradermally, or just beneath the outermost layer of skin, the Food and Drug Administration (FDA) announced Tuesday afternoon. Previously, the vaccine could only be administered subcutaneously, or into the layer of fat below the skin.
The intradermal injection requires only a fifth of the dose used in subcutaneous injections, and produces a similar immune response, according to a 2015 clinical study cited by the FDA in its press release. Although intradermal vaccinations can result in more redness, firmness, itchiness, and swelling at the injection site, the clinical study reported that the injection was less painful and described the side effects as “manageable.”
“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,” said FDA Commissioner Robert M. Califf, M.D. in a press release. “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.”
The FDA’s emergency authorization will also allow minors who are considered at high risk for MPV to be vaccinated subcutaneously.
Some experts and laypeople alike are skeptical about the efficacy of this new vaccination method. The FDA’s decision is based on data from a single 2015 clinical study, and while there are plans to conduct another study on the efficacy of the intradermal strategy, those results are not expected until the fall or winter. Now, it’s unclear whether that trial will proceed, according to the New York Times. Some have also warned that the intradermal method requires slightly more precision, meaning that if a dose is administered incorrectly, the recipient may not have received adequate protection.
Still, the intradermal method has been used successfully in prior mass vaccination campaigns, including for polio and rabies. Dr. Michael Mina, a former assistant professor of epidemiology at Harvard University, took to Twitter last week to further explain the action mechanism of the intradermal injection method. Essentially, the intradermal method works because dendritic cells, which are abundant in skin tissue, are more efficient at generating an immune response.
