Why do some people not catch COVID?

Scientists are trying to unravel the mystery of why some people don’t catch COVID, despite repeatedly being exposed to the virus.

Since the start of the pandemic, millions of people around the world have been infected by COVID. The original strain was highly infectious and the variants that have developed since have been more infectious.

Despite this, some people will never contract the disease no matter how long they’re exposed. Now, researchers are attempting to explain why that is and if there’s anything that can be learnt from these lucky people.

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Research from Imperial College London shows the key to COVID immunity seems to come from an elevated level of white blood cells in the immune system, known as T cells.

These cells develop as part of the body’s defence response when exposed to different viruses. Traditional vaccines work by introducing inactive particles of a virus to your body in order to coax your immune system into producing more T cells.

But people were showing immunity to COVID before vaccines were even available, so where did their T cells come from?

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The answer appears to be from previous exposure to other coronaviruses, of which COVID is just one. Although often used as a synonym for COVID, coronavirus is a broad category of respiratory infections affecting mammals and includes mild forms of the common cold.

“Being exposed to the SARS-CoV-2 virus doesn’t always result in infection, and we’ve been keen to understand why,” says Dr Rhia Kundu, lead author of the college study.

“We found that high levels of pre-existing T cells, created by the body when infected with other human coronaviruses like the common cold, can protect against COVID-19 infection.”

In short, battling other respiratory infections allows your body to develop the type of defences needed to resist COVID when you’re exposed to it.

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The word ‘coronavirus’ is derived from the Latin word ‘corona’ meaning crown or wreath. The name refers to the spiky proteins that protrude from the main virus particle, which the virus uses to attach to cells and infect you.

Besides previous coronavirus infection, a research team from the Karolinska Institute in Sweden identified a peptide – a short chain of amino acids – in the common influenza virus that matches one found in a typical COVID particle.

The Swedish researchers found that this peptide was present in the blood of 68 per cent of all blood donors in Stockholm, suggesting it was widespread in the population, and could be a key reason Sweden was not overwhelmed with COVID cases despite having relatively light restrictions in place.

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Written by Brad Lockyer

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