Omicron: How the killer T cells in our immune system can protect us from severe Covid-19 | United States

A woman is tested for the coronavirus in the Israeli town of Modi’ín.GIL COHEN MAGEN (AFP)

The immune systems of people who have been vaccinated against Covid-19 or who have already contracted the virus and have recovered eliminate the omicron variant before it is able to cause serious disease, according to several preliminary studies in South Africa. South, United States and the Netherlands. Researchers believe this could explain why omicron is causing fewer hospitalizations and deaths in many countries than in previous waves of coronavirus.

All of the studies were based on the analysis of lymphocytes – white blood cells capable of remembering a pathogen and cleaning it from the body for months, years, decades, or even a lifetime. The elite of these white blood cells are the natural killer cells, which identify infected cells and mercilessly destroy them. This prevents a virus from prolonging the infection and causing serious illness. These lymphocytes, known as CD8 or “killer” T cells, work in conjunction with CD4 “helper” cells which help reactivate the immune system against further infection.

A team from the University of Cape Town led by virologist Wendy A. Burgers studied the levels of these lymphocytes in the blood of 90 patients vaccinated with either Pfizer-BioNTech or Janssen, or who had previously contracted coronavirus. The results – still preliminary and not yet peer reviewed – show that 70 to 80% of the CD4 and CD8 T lymphocyte response was maintained compared to previous variants. The researchers also analyzed the plasma of 19 patients hospitalized with the omicron strain. Not all were vaccinated and had not contracted Covid-19 previously. The results showed that the lymphocyte response was just as effective as in patients admitted to hospital with other variants of the coronavirus.

In the United States, a team led by immunologist Alessandro Sette analyzed the white blood cells of 86 people vaccinated with Moderna, Pfizer-BioNTech or Janssen. Preliminary results suggest that up to 80% of the lymphocyte response remains intact against omicron. “These results mean that up to 80% of our police are still patrolling the body,” said Sette, of the La Jolla Institute of Immunology. “We do not yet know what level of protection is sufficient. It depends on whether we are talking about contagion or serious illness. It is likely that this level of lymphocytes will not prevent the former, but will prevent the latter.

In the Nederlands, another preliminary study focused on 60 healthcare workers vaccinated with Pfizer-BioNTech, Moderna, AstraZeneca or Janssen. The results of this research showed that the white blood cell-mediated immunity against omicron is equal to that against other variants.

For now, all we can say is that getting the vaccine is the best thing to avoid getting sick with omicron or any other variant.

Andrew Redd, US National Institute of Allergy and Infectious Diseases

All of this research takes a different angle from the immunity studies that have been done so far, which have focused on antibodies. These proteins are produced after vaccination or infection and can prevent the virus from entering cells. Several studies have shown that the efficacy of antibodies against omicron is considerably lower than that recorded during previous waves of coronavirus.

The new data seems to correspond to what is observed in many countries: the omicron strain is able to infect people who have been vaccinated or who have already contracted Covid-19, but it is less able to escape it. Be careful with white blood cells, which in most cases can still identify and eliminate infected cells before the variant causes serious illness. It would also explain why countries like South Africa recorded up to 80% fewer hospitalizations during the omicron wave than in previous ones. However, it is still too early to assess the full impact of omicron on hospitalizations and deaths.

The South African study is based on infections recorded during the first two weeks of December and, as such, does not reflect what was observed throughout the duration of the omicron wave. There is no more recent data available. “We were exhausted from the 16-hour days and, furthermore, the team was exhausted from omicron infections,” says Burgers. “We have been forced to stop work for two weeks and hope to resume next week,” adds the South African researcher, whose national government recently lifted its curfew after apparently overcoming the peak of the omicron wave .

Many experts now consider omicron the fastest-spreading virus in history. “In South Africa, deaths and disease severity were lower with omicron,” Burgers notes. “But with the large number of cases reported in many countries, many hospitalizations are to be expected in a very short period of time during which many health workers will be missing due to infection. The situation is very serious.

Much of what happens next will largely depend on the level of vaccination. The studies cited also show that a third dose of the vaccine increases antibody levels and restores their ability to prevent infection. “It is still too early to give conclusive data on the severity of omicron infection in different parts of the world,” said Andrew Redd, researcher at the US National Institute of Allergy and Infectious Diseases. His team were among the first to publish research showing that the ability of lymphocytes to defeat the omicron is “virtually intact” despite the number of mutations it has accumulated. “Right now all we can say is getting the vaccine is the best thing to do to avoid getting sick with omicron or any other variant. Everyone should get their shot as soon as possible and be given a booster when needed, ”Redd said.

Marcos López-Hoyos, president of the Spanish Society for Immunology, views all of this data with cautious optimism. “The infection is endemic because the ability of antibodies to neutralize the virus is failing; it’s barely 20%, ”he says. “On the other hand, the lymphocytes analyzed in these studies are able to prevent serious diseases. With protection between 70% and 80%, the vast majority of those infected will not suffer from serious illness. What’s more, a new study shows that a third dose of the vaccine not only increases antibody levels but also CD4 lymphocytes.

These results are similar to what has been observed with other dangerous variants of the coronavirus. Early studies show that omicron was able to escape antibodies generated by vaccines or infection, but data on white blood cells subsequently indicated that immunity to serious disease remained almost fully intact.

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