This pre-print study has been discussed a few times on HN recently [1][2]. Many people are commenting that this paper is flawed by survivorship bias. While it

This pre-print study has been discussed a few times on HN recently [1][2]. Many people are commenting that this paper is flawed by survivorship bias. While it would be useful to know the "cumulative" risk of SARS-CoV-2 infection, the fact is that a vast majority of people survive initial infection. So it is also useful to know the pure risk associated with reinfection - to inform public health policy and vaccine research. That is why the purpose of this research is to evaluate the risk of reinfection by directly comparing the effectiveness of natural immunity and vaccine-induced immunity in the context of the delta variant, which has mutations that confer partial immune escape. This research is significant because it is one of the first and largest studies to do so. [1] https://news.ycombinator.com/item?id=28327482 https://news.ycombinator.com/item?id=28327482 (350 comments) [2] https://news.ycombinator.com/item?id=28317866 https://news.ycombinator.com/item?id=28317866 (226 comments)