A Spanish study has shown for the first time than people with a mild Covid infection they generate a type of immune cell capable of producing antibodies to the coronavirus for the rest of their lives. One of the observations indicated that in infected people the level of antibodies begins to decrease after four months: it is now necessary to understand if the patient develops a complete immune response, which also includes the creation of white blood cells capable of remembering and eliminating the virus even years. after the first infection. Several studies have shown that infected people and those who are vaccinated generate a cellular immune response that protects them from reinfection.
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The new study, published in Nature, brings excellent news: the researchers analyzed 77 patients who had mild or moderate Covid-19 disease. In most of them, they saw that the antibodies drop sharply after four months, but then the reduction is slower and these molecules are still present in the bloodstream for up to 11 months after infection. This research was the first to investigate the presence of long-lived plasma cells in the bone marrow. These cell types are generated when a pathogen enters the body so that they can remember different characteristics of it. In the case of Covid, it is, for example, the Spike protein that the virus uses to infect human cells. After infection, these immune cells travel to the bone marrow and remain there in a latent state. If the virus reappears, the cells return to the bloodstream and start making antibodies against the virus again: research shows that the vast majority of patients who could have their bone marrow removed, i.e. 15 out of 18, have generated this type. of immune cells.
“Plasma cells can last for life”
Ali Ellebedy, immunologist at the University of Washington School of Medicine and lead author of the study, points out: “Long-lived plasma cells can last a lifetime.” The presence of antibodies does not always mean that the person is “immune” to reinfection, although this is more likely to happen. Ellebedy explains that if the antibodies produced by long-lived cells are not enough, the immune system activates the memory B cells that can produce even more antibodies. This work found these cell types in patients, a finding that coincides with previous studies suggesting that immunity mediated by different types of lymphocytes and immune cells probably lasts for years. This is exactly what happens with other infections. Antibodies and memory cells against SARS, another coronavirus that killed 800 people in the early 2000s, last for at least 17 years. With smallpox, more than 50 years after vaccination, people retain B cells that can make antibodies if the virus reappears in their body.
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And the variants?
One question that remains unanswered is whether these types of immune system cells will be able to neutralize the new variants that appear over time. It all depends, says Ellebedy, on how much the genetic sequence of the virus changes. Previous studies have shown that the immune system of those who are infected and vaccinated easily neutralizes the most worrying variants detected so far. There are some types of antibodies that fail to neutralize the virus, but the immune system never plays it all on a card and produces both antibodies against many different virus proteins and memory cells with the same capabilities, so it’s very difficult. for some variants it could escape all of them and, above all, make someone sick again to the point of causing serious health problems or even death. “It is reasonable that this cell type provides lifelong immunity,” says Manel Juan, head of immunology at the Hospital Clínic de Barcelona. “These long-lived cells are one of those that help immunity against other diseases to last for many years,” he adds.
The “third dose” node
And then the question about the third dose of vaccine: «It is not necessary, just as it would not be necessary to vaccinate those who have already had the disease», explains the expert Ellebedy «The problem is that this is a complicated discussion. Who will tell people not to get revaccinated? I think that, even so, there will be people who will not and thanks to the monitoring of these people we will see that probably nothing happens because they do not revaccinate, “he says. Africa González and Marcos López-Hoyos, of the Spanish Society of Immunology, believe it is too early to think about a third dose because protection from the disease is quite likely to be lifelong.