In an cohort study published in JAMA Internal Medicine by Harvey, Rassen, Kabelac et al., the authors looked at more than 3.2 million US patients who obtained SARS-CoV-2  antibody tests and followed the group for results of subsequent nucleic acid testing for the virus.  The proportion of patients with positive PCR tests was initially higher in the group positive for antibodies, a result consistent with post-infection shedding, but then declined steadily over time and ended up being markedly reduced overall in the antibody positive group; after 90 days, 3% of the group without antibodies had a positive NAAT as opposed to only 0.3% of the antibody positive group, a 10-fold reduction.  This study did not go on long enough to help answer the question of how long the reduction in risk persists, but it does support other studies that have found similar decreases in the risk of subsequent SARS-CoV-2 infection following naturally acquired illness. We’ll need more time and data to help sort out how durable the protection from natural illness and vaccines will ultimately be, but these results help reinforce the notion that COVID antibodies can be protective.

Harvey RA, Rassen JA, Kabelac CA, et al. Association of SARS-CoV-2 Seropositive Antibody Test With Risk of Future Infection. JAMA Intern Med. Published online February 24, 2021. doi:10.1001/jamainternmed.2021.0366