To the Editor A recent Research Letter reported that 99% of 295 “COVID-confirmed” participants tested positive for antibodies against the SARS-CoV-2 receptor-binding domain (RBD). Testing performed on cross-sectional samples using a total immunoglobulin assay found no association between time after infection and antibody levels. The authors concluded that “although evidence of natural immunity in unvaccinated healthy US adults up to 20 months after confirmed COVID-19 infection is encouraging, it is unclear how these antibody levels correlate with protection against future SARS-CoV-2 infections, particularly with emerging variants.”
