If they do, they have not published any case reports or papers in the peer-reviewed medical literature. Which is what is typically done to share valid findings.
That doesn't mean it isn't true. First, it may be a bit early to expect peer-reviews and medical publication. Also, covid 19 isn't the only Corona virus, and it is genetically very close to others; it's singular unusual trait seems to be it's much more easily transmited. There is no reason
not to believe there is some immunity resulting from surviving the
Andromeda Strain ...ooooops, I mean covid 19 (I keep making that mistake; silly me
) just from previous experience with what we know.
I'm NOT trying to say there is such immunity, only that I think we have good reason to believe it is happening. Time will tell, I guess.
Another thing; it's typical for viruses to get weaker as time goes on. Killing off hosts is a very bad strategy from a evolution/survival of the organism point of view.