If you’ve had a cold or flu, your Covid-19 symptoms are likely to be far less severe.
It could explain why Covid is usually a mild infection in children, who are often exposed to colds in the classroom, say researchers from Stanford University’s school of medicine. Up to 80 percent of small children encounter cold viruses even in the first few years of life, such as in day care centres.
“A lot of people get sick or die from Covid, while others are walking around not knowing they have it. Why?” asked Mark Davis, one of the researchers. And the answer could be to do with a previous coronavirus infection, which our immune system—and especially our killer T-cells—remember and are primed when we catch the more deadly Covid virus.
People who suffer the worst Covid symptoms also have T-cells that don’t show signs of a previous run-in with a coronavirus, such as the common cold. In blood samples taken from Covid patients, those with the mildest symptoms had many more memory T-cells, which targeted peptides that are shared by all the coronaviruses, including Covid’s SARS-CoV-2. Conversely, those with the most severe symptoms had T-cells that had to learn how to combat the Covid virus, so they were starting from scratch with the coronavirus.
It’s the T-cells that really matter. The focus on antibody levels can be a false flag because antibody proteins are easily fooled by invading viruses. “Pathogens evolve quickly and learn to hide their critical features from our antibodies,” Davis explained.
T-cells are a better indicator and provide a stronger defence from the next coronavirus infection. The cells produce ‘daughter cells’ that retain a memory of a previous infection and persist in our blood and lymph system for more than a decade. “Memory cells are by far the most active in infectious-disease defence. They’re what you want to have in order to fight off a recurring pathogen. They’re what vaccines are meant to generate,” he said.
(Source: Science Immunology, 2021; July 1, 2021; doi: 10.1126/sciimmunol.abg5669)
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