Covid-19: Those infected are capable of generating antibodies against the coronavirus for the rest of their lives | Science

A study has shown for the first time that people with a mild COVID infection produce a type of immune cell capable of making antibodies against the coronavirus for the rest of their lives.

One of the apparently disturbing observations in people infected with SARS-CoV-2 indicated that their level of antibodies – proteins capable of preventing the virus from entering cells – begins to decline after four months. The key is to know if despite the fact that the antibodies fall, the patient has developed a complete immune response, which also includes the creation of white blood cells with memory, capable of remembering and eliminating the virus many months and even years after the first infection. Several studies have shown that this is the case, so that people who pass the infection and those who are vaccinated generate a cellular immune response that protects them against reinfections.

The new job, published in Nature, brings very good news. Those responsible have analyzed 77 patients who had a mild or moderate disease (this is the group about which there were doubts). In most of them, they saw that the antibodies decline sharply after four months, but then the reduction is more slow and these molecules are still present in the bloodstream for up to 11 months after infection.

More importantly, this work was the first to analyze the presence of long-lived plasma cells in the bone marrow. These types of cells are generated when a pathogen enters the body so that they can remember several characteristic features of it. In the case of covid, it is, for example, the S protein that the virus uses to infect human cells. After the 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 begin to make antibodies against the virus again. The work shows that the vast majority of patients who were able to take bone marrow samples – 15 out of 18 – generated this type of immune cells.

Ali Ellebedy, an immunologist at the University of Washington School of Medicine and lead author of the study, highlights: “Long-lived plasma cells can last a lifetime.” These cells “will continue to produce antibodies forever,” he adds.

The presence of antibodies does not always mean that the person is “immune” to reinfection, although this is most likely to be the case. Ellebedy explains that if the antibodies made by long-lived cells aren’t enough, the immune system activates memory B cells capable of making even more antibodies. This work has found these types of cells in patients, a finding that is consistent with previous studies suggesting that immunity against SARS-CoV-2 mediated by different types of lymphocytes and immune cells likely lasts for years. This is exactly what happens with other infections. Antibodies and memory cells against SARS, another coronavirus that killed 800 people at the beginning of the last decade, last for at least 17 years. With smallpox, more than 50 years after vaccination, people retain B cells capable of making antibodies if the virus reappears in their body.

These cells “will keep making antibodies forever,” says Ali Ellebedy, an immunologist at the University of Washington School of Medicine.

A question that remains unanswered is whether these types of cells of the immune system 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 infected and vaccinated smoothly neutralizes the most worrisome variants detected so far. There are some types of antibodies that fail to neutralize the virus, but the immune system never plays everything on a card and produces both antibodies against many different proteins of the virus and memory cells with the same capacities, so that it is very difficult to some variant could escape them all and, above all, make someone sick again to the point of causing serious health problems or even death.

“It is reasonable that this type of cells provide 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 last for many years,” he adds.

A still unanswered question is whether a third dose of the vaccine will really be necessary as the companies that manufacture it have proposed. “For me it is clear that it is not necessary, just as it would not be necessary to vaccinate those who have already had the disease,” explains the expert. “The problem is that this is a complicated discussion. Who is going to tell people not to get revaccinated? I think that, even so, there will be people who do not do it and thanks to the monitoring of these people we will see that probably nothing happens because they do not get revaccinated ”, he says.

Africa González and Marcos López-Hoyos, from the Spanish Immunology Society, think that it is “too early to be thinking about third doses”. “It is quite probable that the protection by disease or by vaccine is for life, although it is something that we are going to have to analyze,” explains López-Hoyos. “You have to be very aware of what happens with very old people and with those with underlying diseases. In any case, we think that the need for a third dose is not as much as the CEOs of Pfizer and Moderna say. The first thing in any case is to vaccinate everyone for the first time. Studies like this show that the immunization generated by the infection is more protective than previously thought ”, he concludes.

The immune system generates cells of short, medium and long duration in response to an infection, explains Africa González, an immunologist at the University of Vigo. “Translated to vaccines, there are some that only give temporary humoral antibody protection for about six months. They are the ones that only carry carbohydrates from bacteria and do not activate T lymphocytes ”, he explains. “Other vaccines induce cellular and humoral responses that are maintained for a few years, such as tetanus, which is recommended every 10 years. With others it is not necessary to vaccinate more after the three doses received in childhood, “he adds.

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