Yet the specific efficacy data for the vaccine is not clear, and some experts argue that not enough is known about how the low-dose intradermal strategy might affect the protection it provides in the real world.
Even at the original dosage size, “there is no traditional assessment of this vaccine,” Dr. Robert Califf, commissioner of the US Food and Drug Administration, said Tuesday. It’s approved for emergency purposes based on studies of immune responses, not clinical outcomes, because there haven’t been smallpox or monkeypox outbreaks large enough to test it.
The intradermal route “may increase the number of available doses in an emergency situation,” the study’s findings say. Last week, the United States declared monkeypox to be a national public health emergency.
US officials said Tuesday that there are plans to collect real-world data on the vaccine and that the National Institutes of Health will launch a clinical trial.
The new federal strategy still calls for two doses of the vaccine given 28 days apart, and it says people who get their first dose subcutaneously can receive their second dose either intradermally or subcutaneously.
But some people have concerns about the shift to a low-dose intradermal strategy.
“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 Tuesday.
“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. This approach raises red flag after red flag, and appears to be rushed ahead without data on efficacy, safety, or alternative dosing strategies.”
The Chicago Department of Public Health said Wednesday that it will be going along with the federal plan to stretch out the supply of monkeypox vaccine by changing to smaller doses given in a different way — but it won’t happen overnight.
“I do think it’ll be a couple of weeks until we’re rolled out more broadly,” Chicago Department of Public Health Commissioner Dr. Allison Arwady said.
Other city health departments, like Columbus Public Health in Ohio, are still reviewing the new federal strategy and what it means for their local response.
“Because this guidance is new, we are currently reviewing it to determine the impact on our vaccine effort, staffing and supplies,” Kelli Newman, a spokesperson for Columbus Public Health, wrote in an email to CNN on Wednesday.
A need for ‘formal clinical efficacy data’
The efficacy of Jynneos for the prevention of monkeypox originally was tested in animals that were exposed to the virus, and it can be inferred from antibody responses seen in people who participated in smallpox clinical studies.
But the Jynneos vaccine was originally developed to contribute to the nation’s defense against smallpox as a bioterrorism response effort — so there still isn’t much data on exactly how well it protects against monkeypox infection, even with a subcutaneous dose.
The FDA approved the Jynneos vaccine in 2019 to prevent smallpox and monkeypox disease, but the approval was mostly to offer a smallpox vaccine option that does not contain live virus. Before then, Sanofi Pasteur Biologics’ ACAM2000 was the only FDA-approved vaccine for the prevention of smallpox. Jynneos has been the preferred vaccine in the current outbreak because ACAM2000 has the potential for more side effects and is not recommended for people with severely weakened immune systems.
“There was no intention of using ACAM2000 or Jynneos for monkeypox,” he said. “Even though they were effective against it, it wasn’t considered something that they were developing it for.”
When Jynneos was approved, FDA officials said its effectiveness for the prevention of smallpox was determined by a clinical study of about 400 healthy adults. Half of them received ACAM2000, and half got Jynneos.
“Although we don’t have clinical efficacy data, it is likely that Jynneos will be highly effective, because of what we know about the smallpox vaccine and because of the efficacy with Jynneos against monkeypox in animals,” Barouch said.
He added that “in general, vaccines are usually more effective at preventing the severe consequences of the disease than preventing acquisition of infection with the pathogen.”
“We can be confident that this will likely be a highly effective vaccine, but the specifics of it in terms of the exact numerical efficacy — and whether that will be prevention of infection or prevention of severe disease — those details are really not known at this point,” Barouch said. “I do think that high-risk people should be vaccinated, but right now, I don’t think it’s possible to give very precise guidance as to exactly what that protection will look like.”
A chance to ‘greatly improve’ availability
“If the vaccine can be administered at lower doses at no risk to effectiveness, lower-dose intradermal injections make sense,” Krause and Borio wrote. “But this strategy could also backfire. If there is a risk to effectiveness, it may be better to focus the available full doses of vaccine on individuals at highest risk — men who have sex with multiple male partners — to provide the best chance of getting the outbreak under control.”
Throughout the outbreak, the vaccine has been given to health-care workers treating people with monkeypox, to close contacts of patients and to people who have been able to find doses at local clinics. The CDC has estimated that at least 1.5 million people in the US are eligible for monkeypox vaccination.
The US Department of Health and Human Services has delivered more than 670,000 doses of the Jynneos vaccine from the Strategic National Stockpile to support local monkeypox response efforts on the ground.
And because of the authorization of intradermal injections, “the 400,000 vials of vaccine in the SNS’s inventory that have been allocated but not yet distributed hold the potential to provide up to 2 million doses using intradermal administration. Additionally, vaccines that have been received by jurisdictions, but not yet administered, are eligible for intradermal administration.”
Lane said the shift to an intradermal strategy could “greatly improve” the availability of vaccine. Her clinic has ordered the shorter syringes needed to administer the vaccine intradermally, the same ones used for tuberculosis testing, she said.
“I ordered those this afternoon,” she said Tuesday, before the FDA issued its authorization.
Lane said many of her patients are worried about getting monkeypox, and she refers them to the ACAM2000 vaccine data as a reference point for how well the Jynneos vaccine may protect against monkeypox.
“What we’re educating people on is that we know from historical data that the ACAM2000 vaccine that was historically given in Africa was about 85% protective against monkeypox. We know that these orthopox families of viruses tend to be responding to the same treatment, as well as the vaccine being somewhat effective,” Lane said.
She added that she does not anticipate any concern around the new vaccination strategy.
“We’re not really seeing any vaccine hesitancy, at least at this point,” she said.
Dr. Paulette Grey Riveria agreed that the intradermal strategy could be an effective way to stretch the supply.
“Scientists are actively studying to determine if immune cells under the skin can activate an antibody response with equal or greater efficiency compared to the subcutaneous route.”
CNN’s Jen Christensen contributed to this report.
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