In order to identify at-risk populations for COVID-19, understanding the effect of serum antibodies on the SARS-CoV-2 virus and susceptibility to the infection is crucial. This study aims to examine the evidence of SARS-CoV-2 infection based on diagnostic nucleic acid amplification test (NAAT) in patients with positive or negative results for antibodies.

This cohort study included a total of 3,257,478 unique patients with a positive or negative index antibody test. The primary endpoints of the study were post-index diagnostic NAAT results, with infection identified as a positive diagnostic test post-index.

Of the 3,257,478 patients included in the study, 2,876,773 (88.3%) had a negative index antibody result and 378,606 (11.6%) had a positive index antibody result. The findings showed that patients with a negative antibody result were older than those with a positive result. Among index-positive patients, 18.4% converted to seronegative during the study period. During the follow-up periods, the ratio of positive NAAT results in individuals with a positive antibody test vs. those with a negative antibody test was 2.85.

The research concluded that patients with positive antibody test results were more likely to have positive NAAT results during the initial phase of the study but less likely to have positive NAAT results over time.