Speaking of immunity, recent research suggests there's crossreactive immunity from other coronaviruses which might explain why there's so many mild or asymptomatic cases, and also suggests vaccines that target the CD4+ T cell responses could work:
There has been a huge amount of uncertainty about immunity to SARS2—both in the context of COVID19 disease pathogenesis and in the context of how to develop a good vaccine.
In the study, 100% of COVID-19 cases made antibodies. 100% of COVID-19 cases made CD4 T cells. 70% of COVID-19 cases made measurable CD8 T cells. We believe these findings are good news, and consistent with normal antiviral immunity.
CD4+ T cell responses to spike, the main target of most vaccine efforts, were robust and correlated with the magnitude of the anti-SARS-CoV-2 IgG and IgA titers. Again, good news.
Additionally, any potential for crossreactive immunity from other coronaviruses has been predicted by epidemiologists to have significant implications for the pandemic going forwards. We detected SARS-CoV-2-reactive CD4+ T cells in ~50% of unexposed individuals.
Detecting SARS2-reactive T cells in ~50% of unexposed people suggests cross-reactive T cell recognition between circulating ‘common cold’ coronaviruses and SARS-CoV-2. This might influence susceptibility to COVID-19 disease.
https://www.cell.com/cell/fulltext/S...674(20)30610-3
https://rattibha.com/thread/1261052353773363200?lang=en
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