On this subject, Yang-et-al (remeber him??) just

He is still using Leronlimab with patients however, their main conclusion is that antibody loss is steep and herd immunity and/or vaccine durability might be challenging.

Quote:

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The protective role of antibodies against SARS-CoV-2 is unknown, but these antibodies are usually a reasonable correlate of antiviral immunity, and anti–receptor-binding domain antibody levels correspond to plasma viral neutralizing activity. Given that early antibody decay after acute viral antigenic exposure is approximately exponential,3 we found antibody loss that was quicker than that reported for SARS-CoV-1,4,5 and our findings were more consistent with those of Long et al.1 Our findings raise concern that humoral immunity against SARS-CoV-2 may not be long lasting in persons with mild illness, who compose the majority of persons with Covid-19. It is difficult to extrapolate beyond our observation period of approximately 90 days because it is likely that the decay will decelerate.3 Still, the results call for caution regarding antibody-based “immunity passports,” herd immunity, and perhaps vaccine durability, especially in light of short-lived immunity against common human coronaviruses . Further studies will be needed to define a quantitative protection threshold and rate of decline of antiviral antibodies beyond 90 days.

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