Reports of reinfection with the coronavirus evoke a nightmarish future: Repeat bouts of illness, impotent vaccines, unrelenting lockdowns — a pandemic without an end.

A case study published Monday, about a 25-year-old man in Nevada, has stoked those fears anew. The man, who was not named, became sicker the second time that he was infected with the virus, a pattern the immune system is supposed to prevent.

But these cases make the news precisely because they are rare, experts said: More than 38 million people worldwide have been infected with the coronavirus, and as of Monday, fewer than five of those cases have been confirmed by scientists to be reinfections.