Are we underestimating how many people are resistant to Covid-19?

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Antibody testing, as we know, was slow to get going and unreliable to begin with, and the results to date suggest that the proportions of populations carrying antibodies to the Covid-19 virus are often in single or low-double digits. New, more sensitive antibody tests that have become available in recent weeks could soon provide a much more accurate picture if deployed widely enough, but there are already hints that the results to date may be underestimates.First there was evidence based on diagnostic testing of postmortem samples from patients who died in December that the virus was circulating in western countries – notably France and the US – about a month earlier than was initially thought. New research shows that another component of the human immune response – T cells, which help orchestrate the antibody response – show memory for coronavirus infection when exposed to Sars-CoV-2, the virus that causes Covid-19.In a paper published in Cell on 14 May, researchers at the La Jolla Institute for Immunology in California reported that T cells in blood drawn from people between 2015 and 2018 recognised and reacted to fragments of the Sars-CoV-2 virus. To determine whether it does would involve following a large number of people who show such cross-reactivity to see if they are protected, if not from infection with Covid-19, then at least from severe forms of the disease.If exposure to other coronaviruses does protect against Covid-19, Gupta says, then variability in that exposure could explain much of the difference in fatality rates between countries or regions. Holding to her hunch, she believes that lockdown was an overreaction and that frontline care and protection of the vulnerable – which should have been a priority from the beginning – should be prioritised now. Heymann remains wary of models, which he says have too often been mistaken for reality in this pandemic, and he awaits more data: “I don’t think anybody can predict the destiny of this virus at this point in time,” he says.

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