For people who have their hands full to get two doses of COVID-19 vaccine, the message from public health officials is clear. Do the second shot if you want full protection.
But the evidence suggests that there may be an exception to this rule. If you are already battling a coronavirus infection, one dose may be enough.
“It has long been rumored that people with pre-existing disease need only one dose to get really long-lasting immunity,” said Dr. George Orger Rutherford, an epidemiologist at UC Infectious Diseases in San Francisco.
And Pfizer-BioNTech և Moderna vaccines require two doses a few weeks apart. The first dose is essentially the immune system’s preference for recognizing or attacking the virus’ colloquial protein, while the second is forcing the immune system to produce a flood of antibodies.
A second dose is needed to get as much protection from the virus as possible, experts say.
There are some exceptions to the rule of two doses. For example, having an immediate or severe allergic reaction to the first dose, but not surviving COVID-19 so far.
However, more and more researchers are finding that SARS-CoV-2 infection can be very similar to the first shot of the vaccine.
Researchers in Seattle և Montreal looked at blood serum samples from people who had recovered from COVID-19 և from other people who had never had a coronavirus infection. Samples were collected before and after vaccination with both Pfizer and Moderna vaccines.
The researchers found that in COVID-19 survivors, a single dose of the vaccine increased antibody levels against several variants of the coronavirus by up to a thousand times, so that a second dose did not provide significant additional benefits. However, people without a history of infection had lower levels of antibodies after two doses of the vaccine than previously infected people after only one. The results were reported in the journal Science last month.
In another recent study, New York researchers looked at serum samples from 110 people, some infected with SARS-CoV-2, some not, and analyzed how their antibody levels differed after receiving the Pfizer or Moderna vaccine.
They found that after just one shot, those who were already infected had antibody levels 10 to 45 times higher than those without a history of infection. Moreover, with that first dose, the mean antibody levels of COVID-19 survivors were more than six times higher than the levels of uninfected people who completed both treatments, according to a report in the New England Journal of Medicine.
The initial hypothesis of these findings prompted Dr. Francis Collins, director of the National Institutes of Health, to observe that “the results increase the likelihood that a single dose may be sufficient for someone already infected with SARS-CoV-2″ antibodies already produced. against the virus. ” However, he added in the blog, “much more research is needed, I definitely do not suggest changing the current proposals.”
New York researchers have found that previously infected people have more symptoms after the first shot than when they were infected. They were also more likely to report other less common side effects of the vaccine, including headache, fatigue, fever, chills, muscle aches, and joint pain.
The French health authorities have already recommended that those who have had a SARS-CoV-2 confirmed infection take just one dose of the vaccine, even if their infection has not caused COVID-19 symptoms.
Collins suggests that the US Food and Drug Administration could follow suit if evidence continues to be gathered. “Such a policy could help expand the supply of vaccines and vaccinate more people faster,” he wrote.
“But for any serious discussion of this option, more data will be required,” he added. “It will also be decided by expert advisors to the FDA’s Centers for Disease Control and Prevention (CDC).”
Rutherford said such a move was possible, but that the CDC “has a lot on its plate.”
Dr. Amesh Adalyan, a senior fellow at the Hopkins Center for Health and Safety, said that as the evidence grows, the CDC is “very cautious” and can wait for more research before supporting change.
“What you would do is change the definition of a fully vaccinated person,” he said. For people with past infections, this will bring them a few weeks closer to the day when they can visit fully vaccinated people without wearing a mask or doing physical distance, among other benefits listed by the CDP.
But in some cases, determining who had the past infection is easier said than done, Adalyan said. Officials had to decide what kind of test results, past or present, qualify as evidence.
“Will it be something they can implement operationally? To say, “Well, this person has an antibody test that shows they are positive, it’s enough for us to say that this person can be fully vaccinated after one dose.” ? And I think that becomes a question. Do people have to dig into that document to say that? ” he said.
If they can work out the details, a policy change will reduce the risk of vaccine shortages. While this may not be a major threat in the United States, which has ordered more doses to vaccinate all its citizens, it certainly affects many other countries around the world that are still waiting for their doses to arrive.
“If you can save all those people the second dose, it will be more doses for the whole world, and it will spread the first doses faster in this country,” said Adalyan.