The decision came after the FDA ruled out — at least for now — the use of alternative vaccines, as well as the option of delaying the second dose of the vaccine by three to six months, the agency said. The FDA letter, obtained by CNN on Saturday, was signed by FDA Commissioner Dr. Robert Califf, and Dr. Peter Marks, director of the FDA’s Center for Biologics Research and Evaluation. The letter cited a 2015 clinical study, which Chaplin authored, in which “subjects who received the vaccine intradermally received a smaller volume (one-fifth) than subjects who received the vaccine subcutaneously.” “The results of this study showed that intradermal administration produced a very similar immune response to subcutaneous (SC) administration,” the letter said. While the intradermal injection method “resulted in more redness, tenderness, itching, and swelling at the injection site, but less pain,” the letter continued, “these side effects were manageable.” The FDA also reviewed other options the agency had considered. However, the use of alternative vaccines to prevent monkeypox “has been deemed either impractical or inappropriate at this time,” according to the letter. Specifically, the ACAM2000 vaccine, which is FDA-approved to prevent smallpox, “may not be appropriate now for a potentially immunocompromised population,” the letter said. The FDA also considered the option of delaying second doses of the vaccine by three to six months, rather than giving the second dose the recommended 28 days after the first. But the agency ultimately decided that there was no data to show that this method would provide sufficient protection and that delaying the second dose could also give people a “false sense of confidence that they were protected against monkeypox when the actual level protection will be unknown and likely inadequate,” the letter said. The federal government’s announcement this week authorizing health care providers to give smaller doses of Jynneos came in an effort to better meet high demand for the vaccine. Top health officials in the Biden administration have made clear in recent days that given the speed of the monkeypox spread — which they declared a public health emergency earlier this month — the US did not have enough vaccine to meet demand. This week’s decision to expand the available Jynneos vaccines was aimed at addressing the limited supply. The FDA’s Dr. Marks said Thursday that there are an estimated 1.6 to 1.7 million people in the U.S. who are now eligible for the two-dose Jynneos vaccine. According to the US Department of Health and Human Services, about 634,213 vials have been sent to jurisdictions since Friday. The low-dose intradermal strategy immediately raised concerns among some public health experts, including the limited amount of research surrounding the new method. “This approach raises red flag after red flag and appears to be rushed forward without data on efficacy, safety or alternative dosing strategies,” David Harvey, executive director of the National Coalition of STD Directors, said in a statement this week. Chaplin, the chief executive of Bavarian Nordic, also raised concerns. CNN reported that Chaplin wrote in a letter Tuesday to Calif and HHS Secretary Xavier Becerra that he had concerns about the “very limited available safety data” on the recently announced vaccination strategy and that a relatively high percentage of people in clinical study — 20% — did not get the second shot. “While we have some reservations, we are trying to find the best way to support [emergency use authorization] collecting additional data and aligning responses to assist state officials in development,” Chaplin wrote. “We are also investing in expanding production capacity at both BN and offsite facilities, with more announcements likely soon.”
