A large number of studies have shown that after recovered SARS-CoV-2 patients will have a certain protective immune response in their bodies, including protective antibodies and T-cell immune responses. However, some close contacts to COVID-19 patients may not get infected because of the limited time, space, and viral load. As a result, their nucleic acid and antibody tests may be negative. Is a certain immune protective response to the new coronavirus produced inside a large number of close contacts?

Director of the State Key Laboratory of Respiratory Disease and Professor Ran Pixin’s research team conducted groundbreaking research on this issue. After testing the SARS-CoV-2-specific T-cells in 90 recovered patients and 69 close contacts, it was found that 58% of close contacts developed SARS-CoV-2-specific CD4+ T cell immunity, 14% of close contacts developed SARS-CoV-2-specific CD8+ T cell immunity. The number, function and proliferation capacity of SARS-CoV-2-specific T cells produced in these close contacts are lower than the corresponding virus-specific T cell responses in recovered patients with COVID-19. The research results were published in the international authoritative journal Nature communication (IF: 12.121).

This founding adds new interpretations to the “herd immunity against COVID-19” and the traditional definition of “COVID-19 infection”. On one hand, a considerable proportion of close contacts have developed T cell immune memory, indicating that the proportion of people who have developed SARS-CoV-2-specific T-cell immune memory is greater than expected, though it is still unclear whether these close contacts can be protected from SARS-CoV-2 in the future. On the other hand, the “infection” of these close contacts is so mild that it does not even form an effective infection in traditional definition (positive nucleic acid and antibody tests). Only through T cell testing can we know whether they are “close contacts” or “infected”. Such a high proportion of these people indicates that the number of people infected with COVID-19 may be larger than expected, and the basic reproduction number may be larger than current numbers. According to Altmetric, in terms of network attention, this article has received a wide range of attention. Among more than 200,000 papers published in the same period, it ranks 46th in terms of network attention, and 10th amongst 34,244 papers since the founding of Nature communication in 2010.

Meanwhile, in preliminary studies, the team also found that the recovery of critically-ill COVID-19 patients is related to T cell activation (Am J Respir Crit Care Med. 2020 Aug 15; 202(4): 606–610.): In the presence of a certain amount of neutralizing antibodies, the higher the level of CD8+ T cell activation, the better the recovery of critically ill patients. This study provides a certain reference for COVID-19 patients with adoptive serum therapy. Adoptive serum therapy may be suitable for critically ill patients with high T cell immunity and few neutralizing antibodies. Currently, the team is conducting further research on the source and features of virus-specific T cell immune memory in close contacts, as well as the factors and time of immune maintenance of recovered COVID-19 patients.

Original paper : https://www.nature.com/articles/s41467-021-22036-z.pdf