Inclusion Criteria:  Cared for at AHF Midtown Manhattan Healthcare Center and followed in the OPERA observational database Active in care in the last 24 months Fully vaccinated against SARS-CoV-2 virus, implemented as 21 days after the second Pfizer or Moderna injections, 21 days after the one J&J injection Received a Roche SARS-CoV-2 Semi-Quant Spike Ig AB test after full vaccination as usual clinical care  Exclusion Criteria:  Unvaccinated or partially vaccinated against SARS-CoV-2 virus Never tested with a SARS-CoV-2 Semi-Quant Total AB test after full vaccination