Lots of recent discussion about #SARSCoV2 re-infections, with 2 pre-prints describing possible examples. To contextualize these re-infections, I& #39;d like to discuss the following papers, which document same-season re-infection with influenza, and re-infection with measles (1/6).

This paper ( https://onlinelibrary.wiley.com/doi/full/10.1111/irv.12668)">https://onlinelibrary.wiley.com/doi/full/... describes an otherwise healthy 9-year old who was infected twice in a 3-month span with H3N2 influenza, without any substantial antigenic change in the virus between the two infections (residue 67 in HA1 not major antigenic site). (2/6)

Although less extensively documented due to being from an earlier era, this paper ( https://www.nejm.org/doi/full/10.1056/NEJM196810102791501)">https://www.nejm.org/doi/full/... describes at least one case (the 16-year old) of a person who appears to have been re-infected with measles virus. (3/6)

But overwhelming evidence ( https://www.nature.com/articles/s41467-019-09652-6)">https://www.nature.com/articles/... that infection with influenza usually protects against re-infection by that subtype for 4-7 yrs, despite viral antigenic drift. And measles immunity is usually lifelong ( http://www.med.mcgill.ca/epidemiology/courses/EPIB591/Fall%202010/mid-term%20presentations/Paper9.pdf)">https://www.med.mcgill.ca/epidemiol... (4/6).

All of this to say: we should pay attention to SARS-CoV-2 re-infections, and assess how frequent they are and why they occur. If they are common that suggests immunity not strong or durable. But recall that #SARSCoV2 is the most intensely surveilled virus in history... (5/6)

... and humans are highly heterogeneous, so until we know the statistical frequency of these re-infections, they should not alarm us any more than the occasional influenza or measles re-infections do (6/6).