(261) Low Antibody Titers Demonstrate Significantly Increased Risk of SARS-CoV-2 Infection in a Highly Vaccinated Population from the National Basketball Association
Background: Clinical and real-world evidence suggest immunity wanes over time, and booster doses are necessary for additional protection against SARS-CoV-2 infection. Booster recommendations currently account for individual-level risks through proxy factors that include age, time since vaccination, vaccine type, and immunocompromised status; however, identifying an objective correlate of immunity could help health care providers understand infection risk and the optimal booster timing.
Objectives: To (1) assess the association between antibody titers and factors including time since vaccination, vaccine type, booster status, and prior SARS-CoV-2 infection, and (2) evaluate the relationship between antibody titers and rate of subsequent SARS-CoV-2 infection.
Methods: Before the start of the 2021-2022 National Basketball Association (NBA) season, players and team staff assessed SARS-CoV-2 antibody titers using the DiaSorin LIAISON SARS-CoV-2 TrimericS IgG assay (the “DiaSorin Assay”), which was chosen due to its correlation with neutralizing antibody assays. All individuals aged 18 and older who opted to measure their SARS-CoV-2 antibody titers using the DiaSorin Assay from September 12, 2021 through December 31, 2021 after having completed their primary SARS-CoV-2 vaccine series were included. Those with confirmed COVID-19 infection or who received a vaccine dose (primary or booster) 14 days before their antibody test were excluded. Individuals were censored on date of booster receipt. Relevant demographic and clinical characteristics (e.g., age, time since receipt of primary vaccine, and prior SARS-CoV-2 infection) were collected as part of the NBA occupational health program.
Results: A total of 2,388 fully vaccinated adults underwent antibody testing. The cohort was 78.2% male, 68.1% aged ≤ 40 years, and 56.4% vaccinated (primary series) with the Pfizer-BioNTech mRNA vaccine. Among the 2,248 individuals not yet boosted at serologic testing, those with titers < 250 AU/mL (adj HR: 2.4; 95% CI: 1.5, 3.7) had higher infection rates compared to those with titers >800 AU/mL.
Conclusions: Findings from this study suggest that serologic testing with an appropriately targeted antibody test can inform individual-level assessments of susceptibility to infection and therefore may serve as a useful guidepost for decision-making on when to get a booster. Whether the logic for a Fall booster, like for seasonal influenza, will hold depends on whether COVID-19 establishes a wintertime peak in transmission and whether the duration of the immune response to the booster matches the duration of COVID-19 transmission.
