I have to agree with the previous poster, quite often citation needed is being used as a passive aggressive form of "countering" an argument (I have to admit to having used it myself). And if, like in this case, the study (which was what the poster claimed existed) comes up as one of the first results in a google search, I find "citation needed" either to be disingenuous or lazy. Just as a test I searched for "SARS-COV-1 immunity" and got quite a few relevant references as first results as well (even though not the exact study mentioned above).

This is HN, so I think we can expect people know how to search google.