This study (from Denmark, and the data is well-collected) included 4M people. Concerning acquired immunity from previous infection, only 72 people out of +11K recovered from the first wave were re-infected during the second wave (~6-8 months later).
"The estimated protection against repeat infection after previous SARS-CoV-2 infection was 80·5% (95% CI 75·4–84·5; table 1)."
The re-infected may have been mostly people over 65, as the discussion at the end of the study determines older (recovered) persons had less vigorous immune responses.
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branchandroot
Just data, no opinion
Date: 2021-09-08 05:35 pm (UTC)https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(21)00575-4/fulltext#seccestitle140
"The estimated protection against repeat infection after previous SARS-CoV-2 infection was 80·5% (95% CI 75·4–84·5; table 1)."
The re-infected may have been mostly people over 65, as the discussion at the end of the study determines older (recovered) persons had less vigorous immune responses.