More people have higher immunity to COVID-19 than suggested by antibody testing.
People with mild symptoms or those showing no symptoms of coronavirus seem to have T-cell-mediated immunity against COVID-19 infection.
Experts say this means that the levels of public immunity to the new coronavirus is greater than found in antibody tests.
Cell-mediated immunity is a type of immune responses in which antibodies are not involved.
T-cells are a type of white blood cell and part of the adaptive immune system.
Killer T-cells will destroy the virus while the other type, which are T helper cells, would organise the attack.
Dr Marcus Buggert, the study’s co-author, said:
“T cells are a type of white blood cells that are specialized in recognizing virus-infected cells, and are an essential part of the immune system.
Advanced analyses have now enabled us to map in detail the T-cell response during and after a COVID-19 infection.
Our results indicate that roughly twice as many people have developed T-cell immunity compared with those who we can detect antibodies in.”
The study ran immunological analyses on a group of people who had either mild symptoms or who were showing no signs of coronavirus infection.
Some of participants were a relative of COVID-19 patients who were exposed to them but showing no symptoms afterwards.
These asymptomatic family members, after spending their holiday in the Alps in March, had returned to Stockholm.
The research team were continuously monitoring and running tests on the patients and their families since they had the disease.
Dr Soo Aleman, the study’s senior author, said:
“One interesting observation was that it wasn’t just individuals with verified COVID-19 who showed T-cell immunity but also many of their exposed asymptomatic family members.
Moreover, roughly 30 percent of the blood donors who’d given blood in May 2020 had COVID-19-specific T cells, a figure that’s much higher than previous antibody tests have shown.”
Patients infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) developed a robust T-cell response and antibody production.
It was more difficult to notice antibody responses in those individuals with mild symptoms, nevertheless many showed a strong T-cell activation.
Professor Hans-Gustaf Ljunggren, study co-author, said:
“Our results indicate that public immunity to COVID-19 is probably significantly higher than antibody tests have suggested.
If this is the case, it is of course very good news from a public health perspective.”
Carrying out COVID-19 antibody tests is much easier than T-cells analysis as it must be done in a specialised laboratory in contrast to a home test kit and drive-through or walk-through test sites.
The study was published in bioRxiv (Sekine et al., 2020).