There is already a decent understanding of documented reinfections. The first such cases came out a year ago, e.g.: https://en.yna.co.kr/view/AEN20200406006700320 , or https://www.jpost.com/health-science/israeli-doctor-reinfect... By the end of last summer there were clear documented cases with secondary infection from a different viral strain than the original one, e.g: https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3681489 The original publication (and the reply that I cite that raises some concerns, but leaves the main argument in place) estimated that the protection from a past infection is about 83%, so significantly smaller than that from the 2-dose mRNA vaccines. https://www.bmj.com/content/372/bmj.n124/rr-0