Evidence is emerging worldwide showing between 20 and 50 per cent of people who have never been exposed to Covid-19 have immune cells that can recognise and react to the virus.
The discovery of T cell cross-reactivity has excited immunologists, who hope it could explain some of the mysteries that surround the virus, such as why some people get so much sicker than others.
But scientists caution that it is not yet clear what the discovery means for human health.
Dr Corey Smith, head of the translational and human immunology laboratory at the QIMR Berghofer Medical Research Institute, said some sections of the genetic codes were virtually identical.
They cause the common cold and are extremely common – more than 90 per cent of people have been exposed to them.
Scientists suspect some people who have been exposed to these viruses develop T cells that can also target SARS-CoV-2.
Monash University’s head of microbiology, Professor Stephen Turner, said that in the best-case scenario, cross-reactive T cells do offer some protection.
“That’s why we might be seeing so much asymptomatic infection. If there is a level of protection, due to previous exposure, you have less symptoms – because you’re limiting the amount of virus that can grow,” he said.
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