I've been reading the discussion on re-infection events, with some now arguing that this is not rare. This is being interpreted at the extremes that protective immunity is not possible. In this thread, I am going to argue that re-infections are rare based on data so far.
First, let's look at our toolbox on how re-infections can be measured w/o sequencing everyone. This Herculean paper on common coronas medrxiv.org/content/10.110… uses Ab responses as surrogates for re-infection. You will see that in the top row, there are periodic spikes in Abs... Image
This means that a person has been productively infected by a same or similar virus, and the immune system revs up again with new Abs. Keep in mind that these data are for common cold-causing coronaviruses, not SARS-CoV-2. However, we now have a dozen+ reports on serology...
Let's look at one of those from Richelle Charles' group medrxiv.org/content/10.110…. What we are looking for are second spikes in Abs, just as in the common corona paper. Nothing obvious to me here. No single report has tons of n, but collectively there are now hundreds of subjects.. Image
Across these studies, I can't find any clear examples of re-infection based on serology. Okay, so maybe you don't buy this as a surrogate measure. Let's instead look at some studies looking for the virus itself...
The Korean CDC followed a group of people who tested PCR positive, then negative, then positive again. None of these people had culturable virus or transmitted to contacts, arguing against re-infection. Keep in mind that this is already a rare subset. cdc.go.kr/board/board.es…
Perhaps you may argue that these are not sensitive enough methods. But this study did all that as above and sequencing, and found no intact viral genomes: medrxiv.org/content/10.110…
So I think we should be making the distinction between what is possible but rare, and what is the norm. The evidence up through these first few months shows that protective immunity is the norm. I am hopeful that vaccines will be able to do the same and maybe even better.
Re-upping this thread with a gentle reassurance--re-infections are *rare*. Estimated 0.01% risk by this paper, which looked at over 100,000 cases. medrxiv.org/content/10.110…

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