ABSTRACT
Importance: Individuals at increased risk for severe outcomes from COVID-19, due to compromised immunity or other risk factors, would benefit from objective measures of vulnerability to infection based on prior infection and/or vaccination. We reviewed published data to identify a specific role and interpretation of SARS-CoV-2 spike-targeted serology testing for such individuals. We also provide real-world evidence of spike-targeted antibody test results, identifying the seronegativity rate across the United States from March 2021 through June 2022. Analysis of antibody test results were compared between post-transplant (ie, immunocompromised) and all other patients tested in the first half of 2022. Finally, specific recommendations are provided for an evidence-based and clinically useful interpretation of spike-targeted serology to identify vulnerability to infection and potential subsequent adverse outcomes. Observations: Decreased vaccine effectiveness among immunocompromised individuals is linked to correspondingly high rates of breakthrough infections. Evidence indicates that negative results on SARS-CoV-2 antibody tests are associated with increased risk for subsequent infection. Results from widely available, laboratory-based tests do not provide a direct measure of protection but appear to correlate well with the presence of surrogate pseudovirus-neutralizing antibodies. The results of SARS-CoV-2 semiquantitative tests have also been associated with vaccine effectiveness and the likelihood of breakthrough infection. The data suggest that "low-positive" results on semiquantitative SARS-CoV-2 spike-targeted antibody tests may help identify persons at increased relative risk for breakthrough infection leading to adverse outcomes. In an analysis of data from large national laboratories during the COVID-19 Omicron-related surge in 2022, results from SARS-CoV-2 spike-targeted antibody tests were negative in 16.6% (742/4459) of solid organ transplant recipients tested compared to only 11.0% (47,552/432,481) of the remaining tested population. Conclusions and Relevance: Standardized semiquantitative and quantitative SARS-CoV-2 spike-targeted antibody tests may provide objective information on risk of SARS-CoV-2 infection and associated adverse outcomes. This holds especially for high-risk populations, including transplant recipients, who demonstrate a relatively higher rate of seronegativity. The widespread availability of such tests presents an opportunity to refine risk assessment for individuals with suboptimal SARS-CoV-2 antibody levels and to promote effective interventions. Interim federal guidance would support physicians and patients while additional investigations are pursued.