The shortage of monkey vaccine doses in the United States, which is expected to last for months, is raising pressing questions about how well and how long a single shot might protect against the virus.
The vaccine, called Jynneos, is approved as a two-dose regimen, but most people at risk of infection are getting one dose – if they can afford it. Now the shortage has federal officials considering a rarely used approach: a so-called sparing-dose strategy, which gives shots that each contain only one-fifth of a single dose.
For most recipients, one shot should be enough to prevent serious illness, and there is some evidence that smaller doses may be effective. But preliminary research suggests that people with HIV or other conditions that weaken the immune system may have less protection than people without such illnesses, according to some experts.
“One dose is better than no dose,” said Dr. Alexandra Yonts, an infectious disease physician at the National Children’s Hospital in Washington, D.C. But people with “HIV and other immunocompromised individuals need to be aware that they may not have an adequate level of protection. from infection, even with vaccination,” she said.
Even two weeks after the shot, with the antibody response underway, immunocompromised people may still need to “use all other precautions to avoid exposure, according to public health guidance,” she said.
The results also suggest that some men should be prioritized for full vaccination. Given the supply constraints, that could be difficult.
Federal officials have ordered nearly seven million doses of Jynneos, but the shots won’t arrive for months. So far, the Biden administration has sent about 600,000 doses to states. He said last week that an additional 800,000 doses were being allocated to states, but the distribution could take weeks.
With shortages, some cities, including Washington and New York, are restricting second doses to stretch their supplies. Officials at the Food and Drug Administration and the CDC disagreed with that 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, Dr. Robert Califf, the commissioner of the FDA, that the agency was now considering authorizing shots that contain only a fifth of the regular dose, which are delivered between layers of the skin instead. of about.
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The FDA would have to grant emergency use authorization for Jynneos to administer it this way.
The dose-saving approach has been used when supplies of other vaccines are in short supply. But giving intradermal shots requires more skill than more traditional immunizations.
One shot 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 scaled-down regimen will be enough to prevent infection, and if so, how long that immunity will 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 has overseen testing of Covid vaccines in special populations.
One oft-cited statistic says that the vaccine is 85 percent effective against monkeys. Those data do not come from the Jynneos trials, but from a small study in 1988 that looked at the incidence of mumps among people who had been vaccinated for smallpox earlier in life.
Jynneos as a smallpox vaccine had not undergone any major clinical trials in humans before it was approved. Instead, the FDA relied on measures of antibody responses in small groups of people after immunization with Jynneos compared to those produced by ACAM2000, an earlier smallpox vaccine.
In studies led by its manufacturer, Bavarian Nordic, two doses of Jynneos produced antibody levels in people that were almost identical to those after a single shot of ACAM2000.
Antibody levels after the first Jynneos shot first rose for two weeks and then remained flat until the second dose four weeks later, when they rose to very high levels – higher than the ones recorded with ACAM2000.
The scientists read that this means that if the second dose does not follow the first dose, the protection may not last long.
“Ideally, a second dose would be done if protection is needed for more than that four-week period,” said Dr. Yonts, who reviewed the data for the FDA as a staff scientist.
She added that it might be reasonable to delay the second dose to eight weeks. “But if it’s going to be like six months, then I think the priority would be more towards those who are more immunocompromised,” she said.
Injecting one-fifth of a regular dose of Jynneos between layers of skin may be effective, as the FDA suggested Thursday, according to limited research. The skin has many more of the immune cells that respond to vaccines.
But the research is very limited. Scientists at the NIH planned to test the dose-saving strategy in a clinical trial that was to begin in a few weeks. It is not clear whether those plans will be shelved or accelerated.
Information on how Jynneos works in people with HIV, especially in those with severe immune problems, was already scarce. In one study in Nordic Bavaria, antibody response to vaccination tended to be reduced: At 28 days after the first shot, 67 percent of those with HIV produced antibodies, compared with 84 percent of uninfected people.
Although Dr. Although the data from that trial was inconclusive, a reduced antibody response is often seen in people who have been given immune vaccines. When evaluating Covid vaccines, for example, researchers found that patients with HIV were more likely to have fatal infections.
“Individuals with severe or moderate immunosuppression 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 the vaccines decreases.”
The CDC and the New York City Department of Health say Jynneos is safe for people with HIV, but the agencies have not addressed its effectiveness in that population.
In contrast, health officials in Britain say that for people who are “HIV positive or have any other condition or treatment that results in a weakened immune system, the vaccine may not protect you as well.”
The vaccine package also notes that people who are immunocompromised may have a “diminished immune response”.
“Two shots could be very important in this population, which is not really happening in the public health response,” said Dr Chloe Orkin, an infectious disease doctor at Queen Mary University of London, as she reference to immunized persons.
But until more doses are available, state and local health departments may have little choice but to stick to scale back regimens.
“In a scarce environment, we must do everything possible to get the benefits of the vaccine to the city as quickly as possible,” said Patrick Gallahue, a spokesman for the New York City health department, in a statement.