The monkeypox vaccine dose shortfall in the United States, which is expected to last for months, raises urgent questions about how well and for how long a single shot can protect against the virus.
The vaccine, called Jynneos, is approved as a two-dose regimen, but most people at risk of infection have been getting a dose, if they can find one. Now, the shortage has led federal officials to consider a little-used approach: the so-called dose-sparing strategy, which administers injections that contain only one-fifth of a single dose.
For most recipients, one injection should be enough to prevent serious illness, and there is some evidence that even smaller doses can be effective. But early research suggests that people with HIV or other conditions that weaken the immune system may be less protected than people without such diseases, according to some experts.
“One dose is better than no dose,” said Dr. Alexandra Yonts, an infectious disease physician at Children’s National Hospital in Washington, DC. But people with “HIV and other immunocompromised people should be aware that they may not have an adequate level of protection.” from infection, even with vaccination,” she added.
Even two weeks after injection, when the antibody response is underway, immunocompromised people may still need to “take all other precautions to avoid exposure, based on public health guidelines,” he said.
The findings also suggest that some men should be prioritized for full vaccination. Given supply constraints, that can be difficult.
Federal officials have ordered nearly seven million doses of Jynneos, but the injections will take months to arrive. So far, the Biden administration has shipped some 600,000 doses to states. He said last week that 800,000 additional doses they were being allocated to states, but distribution could take weeks.
Faced with shortages, some cities, including Washington Y New York, they are restricting second doses to stretch their supplies. Officials from the Food and Drug Administration and the CDC disagree with that strategy, noting that Jynneos is passed as a vaccine to be given in two doses 28 days apart.
But when federal health officials declared a public health emergency Thursday, FDA Commissioner Dr. Robert Califf said the agency was now considering authorizing injections containing just one-fifth of the regular dose, given between Layers of skin. from under her.
What to know about the monkeypox virus
What is monkeypox? Monkeypox is a virus similar to smallpox, but the symptoms are less severe. It was discovered in 1958, after outbreaks occurred in monkeys kept for research. The virus was found mainly in parts of central and western Africa, but in recent weeks it has spread to dozens of countries and infected tens of thousands of people, mostly men who have sex with men. On July 23, The World Health Organization declared monkeypox a global health emergency..
The FDA would have to grant Jynneos an emergency use authorization for it to be administered in this way.
The dose-sparing approach has been used when supplies of other vaccines are in short supply. But giving intradermal injections requires more skill than is needed for more traditional immunizations.
One injection is probably enough to prevent severe symptoms in most people, and the dose reduction strategy may work just as well. But it’s unclear whether a reduced regimen is enough to prevent infection and, if so, how long that immunity might last, federal health officials said.
“We’re in a data-free zone,” said Dr. Emily Erbelding, an infectious disease expert at the National Institutes of Health, who oversaw trials of Covid vaccines in special populations.
An oft-cited statistic says that the vaccine is 85 percent effective against monkeypox. Those data are not derived from the judgments of Jynneos, but from a small study from 1988 which looked at the incidence of monkeypox among people who had been vaccinated against smallpox earlier in their lives.
No large clinical trial of Jynneos as a monkeypox vaccine in humans was conducted prior to its approval. Instead, the FDA relied on measures of antibody responses in small groups of people after immunization with Jynneos. compared to those produced by ACAM2000a previous smallpox vaccine.
In studies conducted by its manufacturer, Bavarian Nordic, two doses of Jynneos produced antibody levels in humans that were about the same as those obtained after an injection of ACAM2000.
Antibody levels after the first Jynneos injection initially increased for two weeks and then remained stable until the second dose four weeks later, when they spiked to very high levels, higher than those recorded with ACAM2000.
Scientists interpret this to mean that if the first dose is not followed by a second, protection may not last.
“Ideally, a second dose would be given if protection is desired for more than that four-week period,” said Dr. Yonts, who reviewed the data for the FDA as a staff scientist.
He added that delaying the second dose to eight weeks might be reasonable. “But if it’s going to be like six months, then I think the prioritization would lean more towards those who are more severely immunocompromised,” she said.
injecting one-fifth of a regular dose of Jynneos between the layers of the skin, as the FDA suggested Thursday, may be effective, according to limited research. The skin has many more immune cells that respond to vaccines.
But research is very limited. NIH scientists had planned to test the dose-sparing strategy in a clinical trial that will begin in a few weeks. It’s unclear if those plans will be shelved or fast-tracked.
Information on how well Jynneos works in people with HIV, particularly those with severe immune problems, was already scarce. In a study conducted by the Bavarian Nordic, the antibody response to vaccination tended to be decreased: By 28 days after the first injection, 67 percent of people with HIV antibodies producedcompared to 84 percent of uninfected people.
Although Dr. Yonts said the data from that trial was inconclusive, a reduced antibody response is often seen among immunosuppressed people who receive other vaccines. In evaluating Covid vaccines, for example, the researchers found that HIV patients were more likely to have advanced infections.
“It is recommended that people with severe or moderate immune suppression receive additional doses of common vaccines,” said Keri Althoff, an epidemiologist at the Johns Hopkins Bloomberg School of Public Health, who led the Covid vaccine study. “As immune suppression increases, the response to vaccines decreases.”
The CDC and the New York City Department of Health say jynneos is safe for people with HIV, but agencies have not addressed its effectiveness in that population.
By contrast, health officials in Britain tell that for people who “are HIV positive or have any other condition or treatment that weakens the immune system, the vaccine may not protect them as well.”
vaccinations insert package It also notes that immunosuppressed people “may have a decreased immune response.”
“Two injections can be very important in this population, which is something that is not really happening in the public health response,” said Dr. Chloe Orkin, an infectious disease physician at Queen Mary University of London, referring to the immunosuppressed people.
But until more doses are available, state and local health departments may have no choice but to stick with the reduced regimens.
“In an environment of shortages, we need to do everything we can to get the benefits of the vaccine to the city as quickly as possible,” Patrick Gallahue, a spokesman for the New York City health department, said in a statement.