US allows fractional dosing of monkeypox vaccine to extend supply
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U.S. officials on Tuesday disclosed a plan to extend the nation’s supply of monkeypox vaccine by allowing providers to deliver it in fractional doses and to open up monkeypox vaccination to children.
Under the plan, providers will be able to draw up to five doses from existing one-dose vials of the Jynneos vaccine without sacrificing its effectiveness. The one-fifth-sized doses will be delivered intradermally rather than subcutaneously to improve the immune response.
The FDA issued an emergency use authorization (EUA) for the fractional dosing for high-risk adults aged 18 years or older. The EUA also allows the vaccine to be administered to children who are deemed at high risk for infection, although they would continue to receive it subcutaneously.
The vaccine, which was approved for use in 2019, will still need to be given in two doses 28 days apart, the FDA said. It said there are no data showing that one dose provides lasting protection.
FDA Commissioner Robert M. Califf, MD, said during a press briefing that the country’s supply of Jynneos has not been able to keep pace with the U.S. outbreak, which has grown to include more than 8,900 cases as of Monday, according to the CDC. HHS Secretary Xavier Becerra declared the outbreak a public health emergency last week.
The new strategy, which means many more people can be vaccinated with the available supply, “is a game changer when it comes to our response and our ability to get ahead of the virus,” said Bob Fenton, the recently named White House monkeypox response coordinator.
In its announcement of the EUA, the FDA cited a 2015 study that showed people who received the vaccine intradermally in two one-fifth-sized doses experienced a similar immune response as those who received it subcutaneously.
“It’s safe, it’s effective and it will significantly scale the volume of vaccine doses available for communities across the country,” Fenton said.
CDC Director Rochelle P. Walensky, MD, MPH, said last week that the U.S. needs enough doses of Jynneos to vaccinate the estimated 1.6 million to 1.7 million people who are at the highest risk for monkeypox, including men who have sex with men.
HHS has made 1.1 million doses of the vaccine available from the national strategic stockpile, and more than 600,000 doses have already been delivered. The new strategy means that the remaining 441,000 vials can produce more than 2.2 million doses, officials said.
Fractional dosing has been used before, including to extend the world’s depleted supply of yellow fever vaccine during outbreaks of the disease in Angola and the Democratic Republic of the Congo in 2016. Study findings showed a high rate of seroconversion among people who received the one-fifth-sized doses.
Walensky said that although intradermal injections are used for other types of vaccines and for tuberculosis skin tests, some health care providers may not be familiar with giving them. She said the CDC will publish interim clinical guidance and post a video on its website to help train providers on intradermal vaccine administration and will hold a Clinical Outreach and Communications Activity, among other initiatives to help roll the strategy out.
Peter Marks, MD, PhD, director of the FDA's Center for Biologics Evaluation and Research, said the decision to continue administering the vaccine subcutaneously to children was made because “it’s a more familiar and simpler” way to do it. He also noted that there are no data on intradermal administration in children.
“It was felt this was going to be the most convenient and familiar [way] for that population,” Califf said.
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