I am continually seeing the poorly informed rumor that people who have recovered from COVID-19 are becoming re-infected with it, usually attached to an article citing a doctor in South Korea.

https://www.reuters.com/article/us-health-coronavirus-southkorea/south-korea-reports-recovered-coronavirus-patients-testing-positive-again-idUSKCN21S15X

There is no evidence at all (thus far) that re-infections are happening.

The "study" in South Korea gives a single RT-PCR test to people who are nearly recovered, and gives them that test again a day or two later. If they test negative on the first test and positive on the second test, the folks in South Korea are calling them "re-infected".

This is not (at this point) what is happening.

People who are nearly recovered are going to have very low viral loads, down near the limit of detection. Under the very best laboratory controlled conditions, if you test 1000 people for SAR-CoV-2 who are still infected but well on their way to recovery, you should expect 50 of them to test negative on one test and positive on the next, because the sensitivity near LOD of those tests is only 95%.

If you hear folks making the claim that people are becoming "re-infected", don't just slap them..

We can't slap people around for this one. If one doesn't understand how PCR works (which is almost everyone) seeing a doctor say things like this is cause for legitimate concern.

You only get to slap them if you point out that the occasionally "test-negative-then-test-positive" is expected and normal and they still try to spread the rumor that people are becoming re-infected.

Also, let's face it: if there is ever a significant non-synonymous mutation in the SARS-CoV-2 spike protein, we really could see reinfections.

Reinfection isn't impossible with a mutation on that particular protein, but there's nothing to suggest that such a thing has happened. We have a pretty good handle on the phylogenetic tree of the wee beastie.