Is immunity possible after having Covid-19?

When we have suffered from an illness like Covid-19 and are still alive, we are left with the uncertainty of how long our immunity will last; even when we are vaccinated, we do not know if the doses administered are sufficient and for how long the antibodies remain in the body.

Studies conducted at Washington University in St. Louis (USA), and published in the journal Nature, state that people who have had mild cases of Covid-19 have immune cells in their bodies months after recovering that pump out antibodies against the virus, and that these cells could persist for a lifetime.

Researchers analyzed a sample of 77 patients who had the infection, most of them mild, and observed that antibodies against the virus declined rapidly in the first four months after infection, and after four months, the decline slowed and became more gradual over the following seven months.

For their study, the team used blood samples, taken at three-month intervals, beginning approximately one month after the initial infection. Most participants had experienced mild cases of Covid-19, and only six had been hospitalized. In addition, bone marrow samples were obtained from some participants at two different times, and samples were also taken from eleven people who had not had the disease.

As a result, antibody levels in the participants' blood declined rapidly in the first few months after infection and then mostly stabilized, with some antibodies detectable even eleven months post-infection. Furthermore, fifteen of the nineteen bone marrow samples from people who had recovered from the disease contained cells producing antibodies specifically directed against the virus. These cells could still be found four months later in the five people who returned to provide a second bone marrow sample.

According to the study, after a viral infection, antibody-producing immune cells multiply rapidly and They circulate in the blood , causing antibody levels to spike. Once the infection is resolved, most of these cells die, so antibody levels in the blood decrease. However, some of them, called long-lived plasma cells , migrate to the bone marrow, from where they continuously secrete low levels of antibodies into the bloodstream.

Initially, it was mistakenly interpreted that immunity was not long-lasting because antibodies decrease after infection; however, it is normal for antibody levels to decrease after an acute infection, but they do not disappear; rather, they stabilize, the researchers clarified. A small population of antibody-producing cells, called long-lived plasma cells, migrate to the bone marrow and settle there, continuously secreting low levels of antibodies into the bloodstream to help protect the body against another viral attack.

The study authors predict that people who were infected with Covid-19 but did not experience symptoms may also have lasting immunity. However, it has not been established that those who suffered from a Those with more severe infections may be protected against a future outbreak. Scientists will now investigate whether vaccination also induces long-lasting antibody-producing cells.

Ramona Ávila Núñez, PhD

Reference:

Turner JS, Kim W, Kalaidina E, Goss CW, Rauseo AM, Schmitz AJ, Hansen L, Haile A, Klebert MK, Pusic I, O'Halloran JA, Presti RM, Ellebedy AH. SARS-CoV-2 infection induces long-lived bone marrow plasma cells in humans. Res Sq [Preprint]. 2020 Dec 31:rs.3.rs-132821. doi: 10.21203/rs.3.rs-132821/v1. Update in: Nature. 2021 May 24; PMID: 33398264; PMCID: PMC7781328.