Protection against covid-19 reinfection could last at least 10 months

BarcelonaResearchers at the Vall d'Hebron Research Institute (VHIR) have found T lymphocytes capable of destroying cells infected by SARS-CoV-2 in the lungs of patients who have recovered from the disease. The finding, published in the journal Nature Communications, confirms that these cells can remain in the lung for up to ten months after infection and offer protection against reinfection.

When talking about immunity to covid, reference is always made to antibodies. But this defence mechanism is neither the only nor the most important defence mechanism the body has against viruses. As has been known since the 1950s, T-lymphocytes are the main source of protection against viral infections. Detecting them in the lungs, however, is difficult because a biopsy is required. During the course of the study in which they analysed these cells, the researchers saw that the T lymphocytes in the patients' blood had markers indicating that they would move to the lungs. They then took lung biopsies from seven recovered patients who had lung biopsies from other causes and, when analysed, confirmed the presence of resident T lymphocytes. Moreover, they were detected both in people who had mild disease and in patients who had had severe covid. In any case, the number of patients is too small to draw definitive conclusions.

"The respiratory tract is the entry route of the virus and, therefore, these cells would give a much faster and efficient response that would limit the spread and also the disease", explains Meritxell Genescà, co-author of the study and principal investigator of the infectious diseases research group at VHIR. "As covid-19 is a lung infection, the immune response goes to the lungs, in this sense it is not surprising", says Manel Juan, head of immunology at Hospital Clínic de Barcelona, who has not participated in the research. "In fact", he adds, "they had already been found in autopsies performed on patients who had died".

This result is not the first evidence of the protection conferred by having passed the disease. The question everyone wants to answer, though, is how long it lasts. "These resident cell types have been studied in patients with influenza, MERS and SARS [two coronaviruses similar to SARS-CoV-2], and it has been seen that they can last five or six years, so they could have a similar life, but for the moment, of course, it has not been proven", says Genescà, who for this reason can only ensure a duration of 10 months from the limited study that has been done. Juan, however, goes further: "Science is not only based on what you do directly but also on what you extrapolate from other information and, from this point of view, there are reasons to think that T lymphocytes can last more than ten years, but we won't know for sure until time goes by". "For the moment, the immunity data we have from both the natural infection and the vaccine are very good", he concludes.