Thread by @profshanecrotty

1/ There are various tweets misinterpreting COVID-19 “pre-existing immunity” and making dangerous claims about herd immunity. Since many of those claims refer to our scientific papers, we will reiterate the facts. @SetteLab @ljiresearch @ScienceMagazine @CellCellPress

2/ Our 1st scientific paper showed that ~50% of unexposed people have T cells that recognized SARS-CoV-2 already doi.org/10.1016/j.cell…. The most obvious conclusion was these were memory T cells from previous common cold coronavirus infections, but that was not directly shown.

3/ Our 2nd paper, very recently published, showed that these were memory T cells from previous common cold coronavirus infections doi.org/10.1126/scienc…. Five other labs have also published related findings doi.org/10.1038/s41577…

4/ These observations about pre-existing T cell immunity (also call "crossreactive immune memory", which avoids the word "immunity" that sometimes gets misinterpreted as “protective immunity” [sorry, immunology is complicated] ) are important because...

5/ ...these memory cells MAY impact people’s responses to SARS-CoV-2 infection, or COVID-19 vaccines.

6/ Therefore, we have pointed out that these coronavirus crossreactive immune memory T cells are important to pay attention to in human COVID-19 studies this year.

7/ We SPECULATE that it is conceivable that these T cells may potentially reduce COVID-19 disease severity, based on things we know about flu and T cells.

8/ 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.

9/ We, and other labs, are working hard on these unanswered questions.

10/ Additionally, even if our most optimistic speculations about crossreactive T cell memory were found to be correct, it would mean that just as many people would get infected with SARS-CoV-2, but fewer would become severely ill and die from COVID-19.

11/ 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.

12/ For people who were asking for more information about masks, extensive data support that masks are one of the most effective interventions to reduce SARS-CoV-2 spread and COVID-19 cases:

13/ One excellent new summary of the scientific and medical literature is: link.springer.com/article/10.100… .

Or if you prefer one study: thelancet.com/journals/lance…

Or if you prefer 70 sources: threader.app/thread/1279144…

14/ But if you prefer a visual aid summarizing the knowledge on masks and COVID-19, National Geographic @NatGeo has you covered: nationalgeographic.com/science/2020/0…