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Do some people have protection against the coronavirus?

August 2, 2020. Summarized by summa-bot.

Why do some people get very sick and even die from Covid-19, while others show few if any symptoms? We know some of the big factors that put people at higher risk of having a severe course of disease, but could certain people actually have some type of protection?

A recently published summary article in the journal Nature Reviews Immunology put forth a tantalizing possibility: A large percentage of the population appears to have immune cells that are able to recognize parts of the SARS-CoV-2 virus, and that may possibly be giving them a head start in fighting off an infection.

about half of the people had some T-cell reactivity," co-author of the paper Alessandro Sette from the Center for Infectious Disease and Vaccine Research at La Jolla Institute for Immunology, told CNN.

It's T cells like those, which reacted to the SARS-CoV-2 virus, that Sette and his co-author Shane Crotty discovered -- quite by accident -- in the blood of people collected several years before this pandemic began.

They speculate that this T cell recognition of parts of the SARS-CoV-2 virus may come in part from past exposure to one of the four known circulating coronaviruses that cause the common cold in millions of people every year.

"Would these memory T cells be helpful for protecting you against Covid-19 disease, that's the huge question," said Crotty.

So, when you say, 'They have T-cell reactivity,' well that could help in some people, it could hurt in others," he said.

"At the same time, some of the very sick people have that immunological history that instead of helping them, makes the immune system throw everything at it, and the net result is that you get this over-exuberant response," he said, referring to the cytokine storm that some of the sickest of the sick with Covid-19 experience.

Certainly, we have not seen an immune response related to T cells in overdrive in the very severe cases," said Sette.

So, assuming that a large portion of the population has some kind of T-cell reactivity to the SARS-CoV-2 virus, what does that mean for vaccine efforts?

Furthermore, Sette said upcoming vaccine trials could help uncover the effect of this T-cell cross-reactivity a lot more cheaply and easily than running other experiments.

"It is a conceivable that if you have 10 people that have reactivity and 10 people that don't have the pre-existing reactivity and you vaccinate them with a SARS CoV-2 vaccine, the ones that have the pre-existing immunity will respond faster or better to a vaccine.

There are also implications for when we might achieve "herd immunity" -- meaning that enough of the population is immune to SARS-CoV-2, thanks either to infection or vaccination, and the virus can no longer be as easily transmitted.

In fact, Sette and Crotty wrote in their paper, "It should be noted that if some degree of pre-existing immunity against SARS-CoV-2 exists in the general population, this could also influence epidemiological modelling . . . "

So, ultimately can it be said that some people have at least partial natural protection from SARS-CoV-2, the novel coronavirus, if they have T-cell cross-reactivity?

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