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Researchers in Hong Kong are reporting the first confirmed case of reinfection with the coronavirus.

“An apparently young and healthy patient had a second case of Covid-19 infection which was diagnosed 4.5 months after the first episode,” University of Hong Kong researchers said Monday in a statement.

The report is of concern because it suggests that immunity to the coronavirus may last only a few months in some people. And it has implications for vaccines being developed for the virus.

A plant extract trumpeted this week as a “cure” for Covid-19 by the leader of a pillow company is untested and potentially dangerous, scientists say.

Getting an antibody test to see if you had Covid-19 months ago is pointless, according to guidelines issued this week by a major medical society.

Many tests are inaccurate, some look for the wrong antibodies and even the right antibodies fade away, said experts at the Infectious Diseases Society of America, which issued the new guidelines.

Because current tests cannot determine if someone is immune, the society said, they “cannot inform decisions to discontinue physical distancing or lessen the use of personal protective equipment.”