<i>> Importantly, we detected SARS-CoV-2−reactive CD4+ T cells in ~40-60% of unexposed individuals, suggesting cross-reactive T cell recognition between circulating ‘common cold’ coronaviruses and SARS-Cov-2</i><p>This is saying that 40-60% of <i>existing</i> immune responses (learned over many years of previous coronaviruses) are also protective against the SARS-Cov-2 virus which causes Covid-19 disease.<p>There is a time-based arms race between virus replication & immune defense. <i>If</i> these subjects are otherwise healthy, their immune system should have a good chance of clearing the Covid-19 virus successfully, because it has a "running start" against the new virus.<p>After recovery, their adaptive immune system should have developed an additional immune response that is customized to defend against Covid-19.
If I understood it right they checked that against two groups of 20 people (40 in total only). The study itself seems super interesting and important but such ridiculously small sample size to me, a layman following COVID-19-related research. Is 40 acceptable in this case? Since they are on Cell.com I suppose it is. Bad sample size in COVID-19 research has been discussed recently already and it is a known problem. Another thing is that the sample size was a hidden lead in page 3 and a figure shown only in page 11 of the paper. I wish scientific papers had something of a "nutrition facts" label with basic info like that in their first page.
This seems weird to me though. New Yorkers should have wide exposure to the common cold due to density, as would people in Wuhan.. why was this sars-cov2 so lethal then?
Does this mean that it was much more contagious than thought, if it spreads so fast while so many already have some immunity? Also, if 1/4 of New York City has already had covid-19, then maybe there is only ~1/4 left who wouldn't have immunity. Which would imply that if all restrictions were lifted (in NYC) the "curve" of new infections would be much lower than the first one.
How do they know for sure people have not been exposed? I don’t see how you could prove definitively that a person wasn’t. And with many cases being asymptomatic they could have had it long ago and not known.