I felt it may worthwhile writing a mini thread about #COVID19 immunity following infection to provide some context to the WHO 'immunity passport' statement and its rapid clarification/retraction.
(1/5) https://twitter.com/WHO/status/1254160937805926405

There is no uncontroversial evidence for reinfection by COVID-19 at this stage. We do not know yet for how long someone infected will be immunised against subsequent infection, though on average it should likely be for a year or possibly more.
(2/5)

Importantly, even if residual immunity is insufficient to protect from #COVID19 re-infection, it is still expected to be protective insofar a secondary infection should lead to far milder symptoms.
(3/5)

The confusion about immunity in the context of ‘immunity passports’ stems mostly from the observation that some patients do not seem to mount a strong antigenic response. As such, despite having been infected, they won't test positive when diagnosed with serological tests.
(4/5)

Whether patients who failed to mount a strong antigenic response upon #COVID19 infection are susceptible to re-infection remains unknown since immunity may still be conferred by other immunological pathways (T-cell immunity).
(5/5)