(BSPOT44) Real-World Trends in SARS-CoV-2 Antibody Levels and Their Link to Subsequent COVID-19 in the United States

Background: Studying changes in SARS-CoV-2 antibody levels over time aids in evaluating epidemic control measures and adding valuable insights into the dynamics of the pandemic.

Objectives: The objective of this study is to assess the SARS-CoV-2 antibody levels over time (2021-2022) in the real-world setting, and assess the association between the antibody levels and subsequent COVID-19 outcomes.

Methods: This retrospective observational study linked two real-world data sources via tokenization: 1) antibody data from the Elecsys® Anti-SARS-CoV-2 S assay obtained from routine clinical testing by Labcorp® laboratories in the US between 2021-04-01 and 2022-06-30; 2) infection and vaccination records of the same subjects captured from PurpleLabTM Open and Closed claims repository. Descriptive statistics of antibody titers were analyzed monthly to understand the trend over time, and by the past infection/vaccination status. Incidence of subsequent COVID-19 outcomes within 12 months of the antibody testing were reported.

Results: In total, 268,844 individuals tested with the Elecsys® Anti-SARS-CoV-2 S assay were included. Over the 15-month study period, the overall SARS-CoV-2 antibody levels increased significantly. In April 2021, about 50% showed non-reactive results ( < 0.8 U/mL; median titer = 0.77 U/mL, interquartile range [IQR] 0.4-61.4). After the wide COVID-19 vaccine rollout in May 2021, median antibody titer rose to 431.8 U/mL (IQR=[23.3, 2240]). The median antibody titer rose over 50% from 969 (IQR=[234.8, 2500]) in November 2021 to 1470 U/mL (IQR=[362.2, 2500]) in January 2022, coinciding with the Omicron variants emergence. By June 2022, median antibody titer increased to 7763 U/mL.
Vaccinated individuals who were not previously infected had a higher median antibody titer (2500 U/mL, IQR=[779, 2500]) compared to those with a prior natural-infection only (1110 U/mL, IQR=[187, 2500]) (p < 0.001). A higher antibody level was associated with a lower risk of COVID-19 outcomes. About 40.3% of individuals with non-reactive results developed COVID-19 within 12 months of the antibody test. The proportion of individuals who developed COVID-19 within 12 months decreased to 16.2% for antibody levels ≥0.8 and < 100 U/mL, 13.2% for antibody levels ≥1000 and < 2500 U/mL, and 7.7% for antibody levels ≥2500 U/mL, respectively (p < 0.001).

Conclusions: The increased antibody levels over time suggest that a growing number of the study population gained immunity via prior infections or vaccinations, which is also associated with the reduced risk of COVID-19 outcomes. The results suggest the relevance of SARS-CoV-2 antibody levels as a valuable surveillance tool during and potentially beyond the pandemic era.