Very intriguing - SARS-CoV-2 pre-existing immune reactivity might exists to some degree in the general population (maybe 20-50%?). It is speculated, but not yet proven, that this might be due to immunity to previous common cold coronavirus. Need to learn more. #COVID19 https://twitter.com/nresearchnews/status/1281561318558961664

2) immune system reactivity means that a person person with previous exposure and immunity to common cold coronaviruses might have partial protection against also the new coronavirus. But how much actual protection is unclear. And they also hypothesize it could make it worse too.

3) good excerpt: “It is plausible that people with a high level of pre-existing memory CD4+ T cells that recognize SARS-CoV-2 could mount a faster and stronger immune response upon exposure to SARS-CoV-2 and thereby limit disease severity”