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From the early days of the pandemic, it has been evident that patients respond differently to SARS-CoV-2 infection, ranging from having no symptoms at all to needing hospitalization. So far, at least 4.7 million people have died from COVID-19 worldwide.
Finding the explanation for this remarkable variability has been a main focus of COVID-19 research. How the immune system responds to the viral infection—depending on age, sex, viral load, genetics, and other known and unknown variables—largely defines the course of the disease. Two elements have emerged as essential: reacting on time and toward the right targets. Not controlling the infection early enough or confounding the self with the enemy can cost the body dearly.
We can think of COVID-19 as a two-step disease, says immunologist Darragh Duffy of the Institut Pasteur in Paris. The first step is when “the immune system is trying to respond ...
