At least six studies have reported the presence of T-cells reactive to SARS-CoV-2 in 20 to 50 percent of people who are not known to have been in contact with the virus.

Until now, people did not seem to have pre-existing immunity to the SARS-CoV-2 virus, but is that really the case? Scientists are now investigating possible immune responses, writes the “British Medical Journal”.

Even in local areas that experienced some of the largest increases in excessive deaths during the coronavirus pandemic, serological tests since the peak of the epidemic show that only about one-fifth of people have antibodies to SARS-CoV-2: 23 percent in New York, 18 percent in London, and 11 percent in Madrid.

Among the general population, the numbers are significantly lower, and many national surveys report single-digit numbers.


Not so new coronavirus?

Given that public health responses around the world are based on the assumption that the virus entered the human population without pre-existing immunity before the pandemic, four data suggest that the virus has, as Mike Ryan, head of emergency situations of the World Health Organization, “a long road to burnout”.

But a series of studies that have recorded T-cells that respond to SARS-CoV-2 and in people who have not been in contact with the virus are now opening up new questions about the true nature of the epidemic.

At least six studies have indicated the existence of T-cells reactive to SARS-CoV-2 in 20 to 50 percent of people who are known not to have been in contact with the virus.

In a study of blood from donors whose samples were collected in the U.S. between 2015 and 2018, 50 percent were found to have T-cell forms that respond to SARS-CoV-2. A similar study was conducted in the Netherlands, and T-cells were found in samples collected long before the pandemic in two out of ten people who were not exposed to the virus.

In Germany, reactive T cells were observed in one-third of SARS-CoV-2 seronegative healthy blood donors (23 of 68). In Singapore, a team of scientists analyzed samples taken from people who had not been in contact with SARS or Covid-19; 12 of the 29 samples taken before July 2019 showed reactivity to SARS-CoV-2, just like seven of the 11 people who were seronegative for the virus. Reactivity has also been observed in the UK and Sweden.

There are solid foundations

Although these studies are small and do not yet provide an accurate insight into the pre-existing immune response to SARS-CoV-2, they are difficult to ignore, and several have been published in the journals Cell and Nature.

Alessandro Sette, an immunologist at the La Jolla Institute of Immunology in California and author of several studies, says: “At the moment, we have several studies showing reactivity on different continents. As a scientist, I know that this is something that has a solid foundation. ”

The researchers are also convinced that they are on the trail of determining the origin of that immune response.

  • Our hypothesis is, of course, that it is immunity derived from common colds that are also caused by coronaviruses – says Daniela Weiskopf, one of the authors of the study, who adds that they showed that the actual immune memory came in part from the common virus colds.

Scientists in Singapore have come to similar conclusions about the role of the common cold virus, but have also indicated that T-cell reactivity may come from some other coronaviruses, perhaps animal ones.

Taken all together, a growing body of scientific work documenting the pre-existing immune response to SARS-CoV-2 may encourage pandemic management to re-analyze some fundamental assumptions about how to measure population sensitivity and monitor the extent of pandemic spread.

Is the immunity of the population underestimated?

Seroprevalence testing, which detects the presence of antibodies, is the preferred method of measuring the ratio of people in a population who have been infected with SARS-CoV-2 and who are therefore somewhat immune, and assessing herd immunity thresholds that give a sense of where the phase of the pandemic we find. Whether we achieve this naturally or by vaccination, it seems that all together it will not be over until we achieve herd immunity.

The fact is that only a small number of people, even in the most affected areas, have antibodies to SARS-CoV-2, which has led many to assume that the pandemic is still far from over. In New York, where only a fifth of those surveyed was found to have antibodies, scientists concluded that “monitoring, testing and seeking contacts remain the main public health strategies.”

“No matter how high the herd’s immunity threshold is, we haven’t approached it yet,” said the World Health Organization.

However, T-cell memory is known to have the ability to affect the severity of the clinical picture and susceptibility to future infections, and T-cell studies have noted pre-existing reactivity to SARS-CoV-2 in 20 to 50 percent of people suggesting that antibodies are incomplete. story.

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