“These data suggest that reinfection with SARS-CoV-2 is rare and occurs in less than 1% of individuals...”











https://twitter.com/EricTopol/status/1372329717928325125 …
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So I'm not saying the researchers could've done a better study using the data at hand, because I love this piece of research, but that to really answer the question we kind of need a different study design altogether
I’m not seeing the selection bias in free-for-all testing but agree on looking longitudinal. But “they need more longitudinal data” can apply to most studies. 
Because people choose themselves whether to get tested. While there may not have been a direct monetary cost, testing is certainly not without secondary costs including time, effort, discomfort, etc...
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