Some People May Have Immunity to Coronavirus without Being Exposed

New findings suggest that the immune systems of some people who have not been exposed to the novel coronavirus can exhibit a degree of response to COVID-19 pathogen. This was published in a study in the journal Nature on Wednesday.

The finding suggest that this can mean that these people experience a less severe form of the disease even if they get COVID-19. This new information may be the first step in understanding different people are experiencing different degrees of the disease.

In the study the scientists found that in 68 healthy adults in Germany who were not exposed to the virus, 35% had T cells in their blood that were reactive to the virus.

What are T cells? These cells are specialized immune cells that help protect body from infection.

This reactivity to T cells suggests that the immune system of that particular person has some experience in fighting such an infection before and has memory cells that might help it fight the new infection.

The researchers suggest that these previous exposures could be to the other endemic coronaviruses. The T cells have memory of fighting against these similar viruses, so it reacts to the new coronavirus pathogen as well.

This ability of the T cells to fight off the new pathogen dur to previous exposure to similar viruses is called cross-reactivity in immunological lingo.

Source: Nature

The study included both 18 COVID-19 patients and 68 healthy subjects. It was seen that T cells reactive to the coronavirus were detected in 83% of the Covid-19 patients.

Right now, the possible implications of this finding are not very well understood, and the researchers wrote in their paper that the impact of these cross-reactive T cells on the outcome of a Covid-19 illness still remains unknown. This is the area that needs more research according to the scientists.

However, many experts are speculating on the basis of these new findings. Many of them suggest that this might be the reason we are seeing differences in disease severity in children and adults.  The pre-existing T cells that exist may be much more numerous or more active in younger age cohorts than in older age cohorts. These findings also may explain why disease is severe in some people and not in other, in the same age group.

Source: Our World in Data

Another important thing that can be seen in this study is that T cell presence does not prevent people from getting infected but may only modulate the severity of infection. This can have far reaching implication sin achieving herd immunity, vaccine and drug development. Till now the focus has only been on antibodies and how they affect long term immunity to the virus.

According to public health experts, almost every person in the world has had some encounter with a coronavirus. This might be the reason why 80 percent of the population is only experiencing mild symptoms of the novel coronavirus infection as well.

Many of the scientists say that they are not surprised by these findings that there is T cell cross reactivity present in people not exposed to coronavirus, as SARS-CoV-2 is the seventh human coronavirus that has been discovered, and four of the human coronaviruses are what we call community-acquired coronaviruses, and together those four are responsible for 25% of our common colds.

Coronaviruses are a big family of viruses. So, it is entirely plausible that the T cells that recognize one member of this family also recognize another member of the family, due to some similar traits.

Cross reactive T- immunity needs more research before any definitive statements can be made.  But this is not the first-time people in scientific community have suggested a certain level of pre-existing immunity among some people to the novel coronavirus.

In a previous paper, it was shown that 20 to 50 percent of unexposed donors displayed significant reactivity to SARS-CoV-2 antigen peptide pools. However, like this current research, the clinical relevance of the reactivity remains unknown.

But one thing that can now be conclusively said is that SARS-CoV-2 pre-existing immune reactivity exists to some degree in the general population. The cause of it still up to debate and requires more research. However, the most likely reason are the common coronaviruses that cause colds.

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