In the UK, they investigated cellular immunity to coronavirus in people who had the infection six months ago, and received encouraging data. T-lymphocytes, which provide long-term protection, “live” longer than antibodies, and their level directly depends on the severity of the disease.
A group of British immunologists for several months tracked the concentration of SARS-CoV-2 specific T cells in the blood serum of adult patients who have suffered mild or asymptomatic coronavirus. T cells (or T lymphocytes) store information about previously acting antigens and contribute to the formation of immunity to infectious diseases.
Experts studied blood samples from 77 women and 23 men of 22-65 years old, who contracted coronavirus in March-April, 44 people were asymptomatic. After six months of observation, the researchers identified T-lymphocytes in each patient, and their level was 50% higher in those who had a mild illness, that is, with symptoms. According to the authors, this may mean that the protective effect directly depends on the severity of the infection. Thus, people who have asymptomatic coronavirus infection may be more susceptible to re-infection. Or conversely, their innate immunity may provide sufficient protection against the virus.
The study authors note that cellular immunity can provide protection against coronavirus even when antibody levels are low. How long it will last and whether it can prevent re-infection is still unknown. This will require more extensive and prolonged observations.
The study has not yet been peer reviewed and has been published as a preprint yet, but it has received a lot of enthusiasm from the scientific community. According to Cardiff University professor Paul Morgan, the work provides “a welcome dose of optimism” about the duration of immunity to coronavirus.
Previously scientists found out, antibodies to coronavirus have no more than 6% of the UK population, and their level has been steadily declining every month. Similar data came from other countries, raising many questions about the duration and stability of the immune response to coronavirus.
The first data on the formation of cellular immunity were obtained by specialists from the Karolinska Institutet in Sweden. The researchers performed immunological analysis of samples from 200 patients. Antibodies were not detected in 30% of those examined, but T cells were detected, and their level was twice as high as in people with antibodies.
Scientists have concluded that the level of herd immunity can be much higher, since all over the world scientists in their estimates rely solely on the number of patients with antibodies. This is not surprising, since the analysis for T cells is more complex and is done manually in specialized laboratories, so mass testing is not possible.