This is an interesting read about the pre-existing immunity discussion.
Another important caveat of these T cell studies is that they have not established that the presence of cross-reactive memory T cells is associated with protection against COVID-19 or with less severe disease in people. While they offer clues that provide a foundation for further studies, scientists are still trying to understand what their actual contribution to the immune response might be, if any.
Indeed, these studies have been misinterpreted and used by some individuals to propagate unfounded claims regarding the level of immunity in the population, including Scott Atlas, a neuroradiologist and senior fellow at Stanford University’s Hoover Institution. Another is ophthalmologist James Todaro, who claimed that these findings indicate that herd immunity could be achieved “once only 10-20% are infected with SARS-CoV-2”, which is much lower than most studies have estimated. Todaro has also appeared in a viral video as part of America’s Frontline Doctors, a group that has spread false claims about the efficacy of hydroxychloroquine against COVID-19.
“These are only speculations (no data) and because of their potential importance, it is key for scientists to test these ideas as quickly as possible. While scientists are racing as fast as possible, sophisticated research like this usually takes a lot of time and resources,” Crotty tweeted.
He also advised against relying on T cells for protection and neglecting to take other precautions. “T cells generally don’t completely prevent infections, they limit disease (make it shorter and/or less serious). Thus, wearing a mask is much more effective than hoping you and the people around you have pre-existing T cell memory. Wearing a mask stops infections,” he explained.
"The article accurately discusses the recent findings about the presence/relevance of T cell response against COVID-19. Indeed, both arms of adaptive immunity, humoral and cellular, contribute in different ways to the body’s fight against viral infections. What remains to be seen and explored in...
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