US reinfection case raises question: how long does Covid immunity last?

Case highlights enduring mysteries, including how long a person’s immune system protects against the virus after an infection

A man in Nevada was infected with Covid-19 in March. He recovered and then tested negative for Covid-19. His would have been an unremarkable story amid a pandemic that has infected millions of people in America – if he had not been infected again less than six weeks later.

The 25-year-old male from the American south-west became what appears to be only the second published case of Covid-19 reinfection in the scientific literature, alongside a case of reinfection in Hong Kong.

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