(262) Association Between Antibody Titer Levels, Time from COVID-19 Vaccine and Booster Receipt Among an Occupational Cohort of Fully Vaccinated Individuals

Publication Number: 1307

Background: Limited evidence exists on the correlation of binding antibody titers and time since vaccination, or durability of antibody levels post booster dose, in the context of COVID-19.

Objectives: Describe the association between days since vaccination, as well as booster receipt, and antibody levels among fully vaccinated individuals.

Methods: This observational study collected real-world evidence from US National Football League (NFL) staff participating in the NFL COVID-19 testing program. Participants completed a medical questionnaire and received two antibody tests between 60-91 days apart using Roche Elecsys® Anti-SARS-CoV-2 S assay for total spike protein (semi-quantitative; max value >2500). Demographics, infection history, vaccination/booster manufacturer and status, and comorbidities were collected. We examined age-adjusted association of time since final dose of initial vaccine regimen and antibody titer < 1000 AU/mL using logistic regression, and change in titer levels by booster status using paired t-test.

Results: In total, 573 study participants consented and completed at least one antibody test; at time of analysis, 383 (67%) completed the second test. At first antibody test, among 290 unboosted persons (median days since final dose 219 [IQR: 202-241, range: 36-323]) with no recorded COVID-19 history, the median titer value was 885 [IQR 517-1604], with 12% of individuals at maximum detectable value and 55% below 1000. The odds of a titer value < 1000 AU/mL (vs ≥1000 AU/mL) increased 19% (OR=1.19, 95% CI: 1.003-1.43) for every 30 days since final dose receipt. Among 130 participants boosted prior to first study test, 99% had titer >2500, and 95% boosted remained at the same titer level or higher at test 2. Those who received a booster between antibody tests had a titer increase (1475.0 [1361.2 to 1588.9]; p < 0.001; n = 144); 98% had a titer >2500 at the second test. Unboosted individuals decreased on average (-89.7 [-316.5-137.1]; p = 0.4; n = 33).

Conclusions: These data indicate a decrease in titers after vaccine receipt and a large increase in immunity after booster dose receipt, as measured by antibody testing. Over half of study participants without a booster or COVID history had titers < 1000 AU/mL. While the correlation between antibody titers and the ability to neutralize Omicron is unknown, higher titer values have previously been associated with lower risk of infection; these results indicate significant vulnerability to COVID-19 among unboosted vaccinated individuals.