COVID-19 survivors may have lifelong immunity

To end the COVID-19 pandemic, it is necessary that most people develop long-term and strong immunity to the causative agent of the disease – SARS-CoV-2.

In the scientific world, there is still no consensus on how long people who have had a coronavirus infection remain immune against a specific virus. But recent scientific findings suggest that immune resistance to SARS-CoV-2 may be longer lasting than previously thought.

How immunity is formed

In order to make it easier to understand what will be discussed further, it is necessary to understand what antibodies are. And this is a special type of protein that helps the body recognize and deactivate viral particles. Antibodies are key elements of immune defense. When a new pathogen enters the body, plasma cells (a type of lymphocyte, part of the immune system) are the first to produce specific antibodies. But these cells are distinguished by a short life and shortly after the virus is eliminated from the body, the plasma cells die.

However, in the human body there are other types of cells responsible for the formation of immunity. They are more durable. For example, memory B-cells, which are found in the blood. They are activated and produce antibodies when re-infected with a pathogen. In addition, there are T cells that enhance the adaptive immunity of the body, as well as BMPC cells that can live in the human bone marrow for decades and, if necessary, “wake up” and produce the necessary antibodies.

Immunity to COVID-19: the mechanism of formation

And now, as for immunity to COVID-19. Not so long ago, the results of a study were published in the scientific journal Cell. ^[1], which shows that most patients who recover from COVID-19 accumulate persistent antibodies and SARS-CoV-250-specific B- and T-cells within 2 days. This discovery makes it possible to make a favorable prognosis regarding the possibility of the formation of stable long-term immunity. However, it is still too early for definite conclusions. For a group of people taking part in the study, scientists plan to follow the next 2-3 years to see how long they will maintain immunity against the new coronavirus.

Primary immune defense against SARS-CoV-2 is manifested by the formation of antibodies that are able to recognize the spike protein of the virus, including the RBD and NTD components of the S1 subunit, at an early stage of pathogen replication. These antibodies are formed from plasma cells upon first contact with a pathogen. But after a few months, due to the short life of plasma cells, the amount of antibodies of the IgG, IgA, IgM groups begins to decline sharply. Previously, it was believed that after recovery from COVID-19, the number of antibodies constantly decreases, eventually reaching minimal levels and, therefore, the ability to resist the SARS-CoV-2 virus also disappears.

But American researchers have extended the observation period for people who have recovered from COVID-19 to 250 days. It turned out that over time, the rate of decay of antibodies to the virus slows down and reaches a plateau. That is, even after a long period of time after recovery, the bodies of people who have recovered from COVID-19, albeit at a low level, still retain antibodies that can become the “first line of defense” in the next encounter with SARS-CoV-2. In addition, scientists have found that these same antibodies increase the human body’s resistance to common human coronaviruses that circulated before the pandemic (betacoronaviruses HKU1 and OC43). Moreover, in those who recovered from COVID-19, antibodies to SARS-CoV-1, which their bodies had not previously encountered, were also found. ^[1].

Observing those who have recovered from COVID-19 for several months, scientists have found that their protective reaction is manifested not only by increased production of antibodies, but also by the activation of T- and B-lymphocytes, which are responsible for immune memory, that is, they create more stable protection against re-infection. ^[2].

Scientists also suggested that the organisms of people who were infected with SARS-CoV-2 will be able to produce antibodies against the pathogen in the course of their later life, since specific BMPC cells are also stored in their bone marrow in a “sleeping” mode. ^[3].

How long can immunity last

Despite the inspiring results of research, scientists are in no hurry to draw unambiguous conclusions. It will take a lot of time for experts to be able to accurately determine how long persistent immunity to SARS-CoV-2 lasts, whether there is a difference in the strength of the immune response in people who have had a mild form of COVID-19 and a severe one, whether the immunity developed is different after illness and vaccination.

There are still a lot of questions about SARS-CoV-2. However, today we know many times more about the new coronavirus than in the first months of the pandemic.

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