Does previously infected covid-19+ person cannot get re-infected? What do we know about 'immunity passports' or 'risk-free certificates'?
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#COVID2019

From WHO: After reviewing the evidence on antibody responses to SARS-CoV-2 infection.

1. Studies show that people who have recovered from infection have antibodies to the virus.

2. Despite that the Korean sample suggested the re-infected had little or no infectivity...

...3. Some re-infecteds have low neutralizing antibodies in their blood suggesting that cellular immunity may be critical for recovery.
4. As of 24 April, no study to suggest that the presence of SARS-CoV2 antibodies confers immunity to a subsequent re-infection in humans.

Source and references https://www.who.int/news-room/commentaries/detail/immunity-passports-in-the-context-of-covid-19