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Studies suggest people who have taken Covid-19 should receive a single dose

Nearly 30 million people in the United States – and probably many more whose disease has never been diagnosed – have so far been infected with the coronavirus. Should these people still be vaccinated?

Two new studies answer this question with a definite yes.

In fact, research suggests that for these people, a single dose of the vaccine is enough to stimulate their antibodies and destroy the coronavirus – and even some more infectious variants.

The results of these new studies are consistent with the findings of two others published in recent weeks. Taken together, the research suggests that people who have had Covid-19 should be immunized – but a single dose of the vaccine may be enough.

“I think this is a very good reason why people who have already been infected with Covid should get the vaccine,” said Jennifer Gommerman, an immunologist at the University of Toronto who was not involved in the new research. .

A person’s immune response to a natural infection varies widely. Most people produce large amounts of antibodies that persist for several months. But some people who had mild symptoms or no symptoms from Covid-19 produce few antibodies, which quickly drop to undetectable levels.

Vaccines “even the playing field,” Dr Gommerman said, so anyone who has recovered from Covid-19 produces enough antibodies to protect themselves against the virus.

The latest study, which has not yet been published in a scientific journal, analyzed blood samples from people who have had Covid-19. The results suggest that their immune system would have difficulty repelling B.1.351, the variant of the coronavirus first identified in South Africa.

But an injection of the Pfizer-BioNTech or Moderna vaccine made a big difference: It increased the amount of antibodies in their blood a thousandfold – “a massive, massive increase,” said Andrew T. McGuire, immunologist at Fred Hutchinson. Cancer research center in Seattle, who led the study.

Flushing with antibodies, samples from all participants could neutralize not only B.1.351, but also the coronavirus that caused the SARS outbreak in 2003.

In fact, the antibodies seemed to perform better than those of people who had not had Covid and had received two doses of a vaccine. Several studies have suggested that the Pfizer-BioNTech and Moderna vaccines are about five times less effective against the variant.

Researchers obtained blood samples from 10 volunteers in the Seattle Covid Cohort Study who were vaccinated months after contracting the coronavirus. Seven of the participants received the Pfizer-BioNTech vaccine and three received the Moderna vaccine.

Blood drawn approximately two to three weeks after vaccination showed a significant increase in the amounts of antibodies compared to samples taken before vaccination. Researchers don’t yet know how long the increased amount of antibodies will persist, but “let’s hope they last a long time,” said Dr. McGuire.

The researchers also found an increase in immune cells that remember and fight the virus, Dr. McGuire said. “It seems pretty clear that we are strengthening their pre-existing immunity,” he said.

In another new study, researchers at New York University found that a second dose of the vaccine did not add much benefit at all for people who have had Covid-19 – a phenomenon that has also been observed with vaccines against other viruses.

In this study, most people had been infected with the coronavirus eight or nine months earlier, but saw their antibodies increase from one hundred to one thousand fold when given the first dose of a vaccine. However, after the second dose, the antibody levels did not increase any further.

“It’s a real testament to the strength of immunological memory that they are given a single dose and have a huge increase,” said Dr. Mark J. Mulligan, director of the NYU Langone Vaccine Center and lead author of the study. .

In some parts of the world, including the United States, a significant minority of the population has already been infected, Dr. Mulligan noted. “They should definitely be vaccinated,” he said.

It is not known whether the 1,000-fold spike in antibody levels recorded in the lab will occur in real settings. Yet research shows that one stroke is enough to increase antibody levels significantly, said Florian Krammer, an immunologist at the Icahn School of Medicine at Mount Sinai in New York City.

Dr Krammer led another of the new studies, which showed that people who had Covid-19 and received a dose of a vaccine experienced more serious side effects from the inoculation and had more antibodies than those that had not been infected before.

“If you put the four documents together, it provides very good information about people who already had an infection that required just one vaccination,” said Dr Krammer.

He and other researchers are trying to persuade scientists at the Centers for Disease Control and Prevention to recommend a single dose for those who have recovered from Covid-19.

Ideally, these people should be monitored after the first stroke in case their antibody levels drop after a few weeks or months, said Dennis R. Burton, an immunologist at the Scripps Research Institute in La Jolla, Calif.

The fact that the supercharged antibodies seen in the new study could fight off the 2003 SARS virus suggests that a single dose of the vaccine may have caused the volunteers’ bodies to produce “largely neutralizing antibodies” – immune molecules capable of attacking a wide range of viruses, said Dr Burton.

He and other scientists have researched for decades whether large-scale neutralizing antibodies can fight multiple versions of HIV at once. HIV mutates faster than any other virus and escapes most antibodies quickly.

The new coronavirus mutates much more slowly, but there are now several variants of the virus that appear to have evolved to be more contagious or to thwart the immune system. The new study could provide clues as to how to make a single vaccine that stimulates the production of large-scale neutralizing antibodies that can destroy all variants of the coronavirus, Dr Burton said.

Without such a vaccine, scientists will have to fine-tune the vaccines whenever the virus changes significantly. “You’re stuck in some sort of Whac-a-Mole approach,” he says. It will probably take several months, if not more, to develop and test this type of coronavirus vaccine, but “this is the longer term way to approach this virus.”

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