Antibodies to Sars-CoV-2 developed after infection decrease at different rates: while for some individuals they last few days, for others they will persist for decades. These are the conclusions of a new study that states how the severity of the Covid-19 infection could be a decisive factor in having a longer lasting protection against reinfection. The research, published in The Lancet Microbe journal, found that cured patients with low levels of neutralizing antibodies can still be protected from reinfection if they have robust immunity in the form of T cells (we also wrote about it HERE)
The forecasts on protection
In the study, scientists from the Duke-Nus Medical School of the National Center for Infectious Diseases followed 164 patients with Covid-19 from six to nine months, analyzing their blood for neutralizing antibodies against Sars-CoV-2 ei memory T lymphocytes, the molecules that recognize and signal the cells infected by the virus to the immune system and that can intervene to eliminate them. The scientists then used this information to train a algorithm of machine learning to predict people’s neutralizing antibody trajectories over time.
The classification of antibodies
Based on the analysis, the researchers classified the people into five groups depending on the duration of their antibodies. The first group included those who never developed detectable neutralizing antibodies, also called negative group, and included 11.6% of patients in the study. The group rapidly decreasing, which included 26.8% of patients, had variable initial antibody levels that declined rapidly. The group slowly waning, which included 29% of the participants, mostly tested positive for antibodies six months after infection. The group persistent, which includes 31.7% of individuals, showed small changes in antibody levels for up to 3 months. A minority group (1.8%), delayed response showed a significant increase in neutralizing antibodies during late convalescence.
The role of T lymphocytes
This study shows that the longevity of functional neutralizing antibodies against SARS-CoV-2 can vary considerably and important a monitoring at the individual level said Professor Wang Linfa, co-author of the study and our work could have implications for immunity longevity after vaccination. According to the study, patients, including those in the negative group, showed sustained T cell immunity six months after initial infection, indicating that individuals can still be protected if they have robust T cell immunity, even when the neutralizing antibody level is low. Our study looks at neutralizing antibodies that are important for Covid protection and we found that antibodies against Sars-CoV-2 decrease at different rates, he commented. David Lye of the National Center for Infectious Diseases of Singapore. However, the presence of T-cell immunity provides hope for long-term protection that will require more study and time for confirmation of epidemiological and clinical evidence.
Long-term immunity
Another study by the La Jolla Institute for Immunology published in late January in Science Immunology and devoted to the role of T lymphocytes concluded that subjects suffering from severe cases of Covid they may have a more marked long-term immunity thank you to the increased release of memory protective T cells, necessary to fight reinfection. Scientists found weaker CD8 + T cell responses (responsible for destroying virus-infected host cells) in mildly infected patients. (a phenomenon known as T cell depletion). In seriously ill subjects, however, the response of CD8 + T cells was much more intense. The investigation was based only on blood samples and the T cells in the tissues most affected by the virus (for example the lungs) will be studied.
March 28, 2021 (change March 28, 2021 | 11:28)
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