The shortage of monkeypox vaccine doses in the United States, which is expected to last for months, raises urgent questions about the quality and duration of a single injection can protect against the virus.
The vaccine, called Jynneos, is approved as a two-dose regimen, but most people at risk of infection have received one dose – if they can find it. Now the shortage has led federal officials to consider a rarely used approach: a so-called dose-sparing strategy, which gives injections that each 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 lower doses may be effective. But preliminary research suggests that people with HIV or other illnesses that weaken the immune system may be less protected than people without such illnesses, some experts say.
“One dose is better than none,” 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 the shooting, when the antibody response is underway, immunocompromised people may still need to “take all other precautions to avoid exposure, in accordance with public health guidelines,” she said. declared.
The results also suggest that some men should be prioritized for full vaccination. Given supply constraints, this can be difficult.
Federal authorities have ordered nearly seven million doses of Jynneos, but the vaccines won’t arrive for months. So far, the Biden administration has shipped about 600,000 doses to states. He said last week that 800,000 more doses were being allocated to states, but distribution could take weeks.
Faced with shortages, some cities, including Washington and New York, are restricting second doses to stretch their supplies. Food and Drug Administration and CDC officials have frowned on this strategy, noting that Jynneos is approved as a vaccine to be given in two doses 28 days apart.
But as federal health officials declared a public health emergency on Thursday, FDA commissioner Dr. Robert Califf said the agency is now considering authorizing injections containing only one-fifth of the usual dose, given between the layers of the skin instead. from below.
What to know about the Monkeypox virus
What is monkey pox? 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 has mainly been found in parts of West and Central Africa, but in recent weeks it has spread to dozens of countries and infected tens of thousands of people, overwhelmingly men with sex with men. On July 23, the World Health Organization declared monkeypox a global health emergency.
The FDA would have to grant Jynneos emergency use authorization for it to be administered in this way.
The dose-sparing approach has been used when stocks of other vaccines are scarce. But giving intradermal injections requires more skill than more traditional vaccinations.
One injection is probably enough to prevent severe symptoms in most people, and the dose-sparing strategy may work just as well. But it’s unclear whether a reduced diet is enough to prevent infection, and if so, how long that immunity may last, federal health officials said.
“We’re in a dataless zone,” said Dr. Emily Erbelding, an infectious disease expert at the National Institutes of Health who has overseen testing of Covid vaccines in special populations.
An oft-quoted statistic states that the vaccine is 85% effective against monkeypox. These data are not from Jynneos trials, but from a small 1988 study that looked at the incidence of monkeypox in people who had been vaccinated against smallpox earlier in life.
No large clinical trials of Jynneos as a monkeypox vaccine were conducted in humans prior to its approval. Instead, the FDA relied on measurements of antibody responses in small groups of people after immunization with Jynneos compared to those produced by ACAM2000, an earlier 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 after an injection of ACAM2000.
Antibody levels after the first shot of Jynneos first increased for two weeks and then remained stable until the second dose four weeks later, when they climbed to very high levels – above those recorded with ACAM2000.
Scientists interpret this to mean that if the first dose is not followed by a second, the protection may not last long.
“Ideally, a second dose would be given if protection for longer than four weeks is desired,” said Dr. Yonts, who reviewed the data for the FDA as a scientist.
She added that delaying the second dose to eight weeks might be reasonable. “But if it’s around 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 on Thursday, may be effective, according to limited research. The skin contains many more immune cells that respond to vaccines.
But research is very limited. NIH scientists had planned to test the dose-saving strategy in a clinical trial that was to begin in a few weeks. It is not known if these plans will be suspended or accelerated.
Information about how Jynneos performed in people living with HIV, especially those with severe immune problems, was already scarce. In a study conducted by Bavarian Nordic, the antibody response to vaccination tended to decrease: 28 days after the first vaccine, 67% of HIV-positive people produced antibodies, compared to 84% of uninfected people.
Although Dr. Yonts said the data from this trial were inconclusive, a reduced antibody response is often seen in immunocompromised people receiving other vaccines. When evaluating Covid vaccines, for example, researchers found that HIV-positive patients were more likely to have breakthrough infections.
“People with severe or moderate immunocompromises are recommended for 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 New York City Department of Health say Jynneos is safe for people living with HIV, but the agencies have not addressed its effectiveness in this population.
By contrast, health officials in Britain say that for people who are “HIV-positive or have any other disease or treatment that causes a weakened immune system, the vaccine may not protect you as well”.
The vaccine package insert also states that immunocompromised people “may have a diminished immune response.”
“Two injections can be very important in this population, which does not actually happen in the public health response,” said Dr Chloe Orkin, an infectious disease physician at Queen Mary University of London, referring to the immunocompromised people.
But until more doses become available, state and local health departments may have no choice but to stick to reduced regimens.
“In an environment of scarcity, we must do everything we can to get the benefits of the vaccine to the city as quickly as possible,” New York Department of Health spokesman Patrick Gallahue said in a statement. .