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WASHINGTON -- The Biden administration took steps Tuesday to quintuple the available doses of monkeypox vaccine by authorizing its use intradermally in adults, while also authorizing use of subcutaneous vaccine in children.

"Given the continued spread of the monkey pox virus at a rate outpacing the availability of our current vaccine supply, the agency began exploring viable scientific options that would allow for greater access to the currently available vaccine," FDA Commissioner Robert Califf, MD, said on a call with reporters.

"After conversations over the past several days with key federal partners, the infectious disease community, and Bavarian Nordic, today the FDA has issued an emergency use authorization (EUA) allowing healthcare providers to use an alternative dosing regimen of the Jynneos vaccine," he continued. "This will increase the total number of doses available for use by up to five-fold."

"The EUA also allows for use of the vaccine and individuals younger than 18 years of age determined to be at high risk of monkey pox infection," Califf added. "In these individuals, Jynneos is administered by subcutaneous injection."

He noted that the agency and the CDC "were able to quickly adapt and address the needs of dozens of young children following a monkeypox exposure at a child care facility in Illinois."

Bob Fenton, the White House monkeypox response coordinator, called the announcement of intradermal use a "game-changer" for the administration's vaccine response.

"It's safe, it's effective, and it will significantly scale the volume of vaccine doses available for communities across the country," Fenton said, adding that in addition to the 670,000 vials of the Jynneos vaccine that have already been distributed, "we have 400,000 vials in the Strategic National Stockpile that [are] ready to be ordered, when jurisdictions use 90% of their current supply. With today's announcement, those 400,000 vials have the potential to provide up to 2 million doses to Americans. We encourage jurisdictions to utilize the alternative dosing method as quickly as possible."

As to the scientific basis for the two-dose intradermal vaccine regimen, Califf cited data from a of the Jynneos vaccine used for its FDA approval in 2019.

The study "evaluated a two-dose series given intradermally compared to subcutaneously," Califf explained. "Individuals who received the vaccine intradermally received a lower volume -- 1/5 -- than individuals who received the vaccine subcutaneously. The results of this study demonstrate that intradermal administration produces similar immune response to subcutaneous administration." And although the intradermal administration patients had mild to moderate side effects, including redness, firmness, itchiness, and swelling at the injection site, "these were all manageable," he said.

Even though the agency is granting a temporary unapproved use of an approved product, "the FDA is still assuring high standards for safety and manufacturing quality," Califf added.

Peter Marks, MD, PhD, director of the FDA's Center for Biologics Evaluation and Research, said that giving the vaccine intradermally "is not at all new ... In Germany, this vaccine was given intradermally originally in an effort to replicate the original version of a smallpox vaccine. It's been given to thousands of people intradermally." As for limiting use in children to a subcutaneous vaccine, Marks said that method "is a much more facile way of getting those children vaccinated; it makes it much easier for providers."

CDC Director Rochelle Walensky, MD, MPH, gave an overview of the administration's physician outreach on the intradermal use of the vaccine. "Today, [the CDC] will post interim clinical considerations, distribute a clinician alert message, present this vaccine administration strategy to the Association of State and Territorial Health Officials, conduct outreach to key clinician partners, and post an educational resource video on this new monkeypox vaccine administration strategy," she said.

The CDC will also have its own interim clinical considerations "to provide guidance for the use of the Jynneos vaccine as an intradermal regimen for adults, as well as the standard or subcutaneous regimen for children," Walensky noted.

" will also include an overview of both available vaccines, planning considerations for health departments, including health equity, vaccine administration schedule and dosing regimens, dosing intervals, contraindications and precautions, as well as pre- and post-vaccination counseling," she said. "CDC will also be conducting a series of webinars and training opportunities to educate clinicians on how to appropriately administer the Jynneos vaccine." Walensky also urged healthcare providers to .

During a question-and-answer session, Califf was asked whether there would be any ongoing evaluation of the vaccine's safety and effectiveness. "I want to point out there is no traditional assessment of this vaccine -- it's approved for emergency purposes based on the immunological response, not on clinical outcomes, because there weren't smallpox cases, and the monkeypox outbreaks before this were not large enough to really do a clinical trial," he said.

"So the immunologic response with the intradermal approach is exactly the same as with [subcutaneous vaccine]," Califf continued. "Nevertheless, in either case, we want to collect outcome data, as we do with all vaccines and I'd also point out that the NIH will be mounting a clinical trial and is working through the logistics of that now." For its part, the CDC is also planning to collect data, Walensky said.

Some healthcare providers are concerned that the evidence presented so far is too scant for an EUA. "While we appreciate that the federal government is finally willing to look for solutions to help rectify the shortage of vaccines, no effort to protect people's health should come without proper due diligence and research," David Harvey, executive director of the National Coalition of STD Directors, said in a statement.

"We have grave concerns about the limited amount of research that has been done on this dose and administration method, and we fear it will give people a false sense of confidence that they are protected," Harvey noted. "This approach raises red flag after red flag, and appears to be rushed ahead without data on efficacy, safety, or alternative dosing strategies."

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