Covid-19: Do many people have pre-existing immunity? | The BMJ

Covid-19: Do many people have pre-existing immunity? | The BMJ: It seemed a truth universally acknowledged that the human population had no pre-existing immunity to SARS-CoV-2, but is that actually the case? Peter Doshi explores the emerging research on immunological responses

Even in local areas that have experienced some of the greatest rises in excess deaths during the covid-19 pandemic, serological surveys since the peak indicate that at most only around a fifth of people have antibodies to SARS-CoV-2: 23% in New York, 18% in London, 11% in Madrid.123 Among the general population the numbers are substantially lower, with many national surveys reporting in single digits.

With public health responses around the world predicated on the assumption that the virus entered the human population with no pre-existing immunity before the pandemic,4 serosurvey data are leading many to conclude that the virus has, as Mike Ryan, WHO’s head of emergencies, put it, “a long way to burn.”

Yet a stream of studies that have documented SARS-CoV-2 reactive T cells in people without exposure to the virus are raising questions about just how new the pandemic virus really is, with many implications.

At least six studies have reported T cell reactivity against S