Case of man reinfected with coronavirus stokes immunity fears

A young man has been diagnosed with coronavirus more than four months after he recovered from a first episode of the disease, suggesting that immunity to the virus can be short-lived and raising more questions about vaccines against Covid-19.

The case in Hong Kong is the first lab-confirmed reinfection. Genetic sequencing by scientists at the University of Hong Kong established that the second episode, in an otherwise healthy young man, was caused by a slightly different strain. Researchers had hoped that the man’s immune system would still have recognised and...