This probably explains why Covid-19 infection rates never get much above 20 percent–a large part of the population is already immune. From Tyler Durden at zerohedge.com:
Much of the talk about the coronavirus over the last couple of months has been about antibodies.
They are looked at as part of the key to unlocking questions about immunity to the virus. Specifically, researchers have looked at how vaccines induce antibody responses and how long antibody protections last after someone has had the virus. In the answers to those questions lies the answer to another: how and when will we achieve herd immunity?
There had been worries about coronavirus antibodies over the past few months, as several studies showed they may only last several months. This had led to a litany of questions about how often one would require a vaccination and whether or not we would ever become immune to the “novel” virus.
But on Friday, a new study highlighted by Business Insider shifted focus away from antibodies and onto memory T cells – the cells that identify and destroy infected cells and inform B cells how to craft antibodies.
The study, published in Cell, now suggests that everyone who gets COVID-19 develops T cells that may offer long term immunity by hunting down the coronavirus at later dates. “Memory T cells will likely prove critical for long-term immune protection against COVID-19,” the study says.