Anti-S-Rbd Titer and Risk of Clinical Progression in Patients with Covid-19 Pneumonia

ABSTRACT

Background: Antibodies (Ab) against the receptor-binding-domain of the spike protein (anti-S-RBD) elicited by SARS-CoV-2 infection or vaccination are deemed to be a correlate of protection. We aimed at assessing whether anti-S-RBD titer is associated with the outcome of subjects hospitalized with COVID-related pneumonia. Method(s) Adults hospitalized between Jul 2021 and Jul 2022 for COVID-19 with respiratory failure (SpO2 < 93% on room air) or radiological evidence of pneumonia were included if anti-S-RBD titer was measured within 72h of admission. Time between admission and death/need for intubation was described using Kaplan-Meier curves. Cox Regression analysis, stratified by vaccination status, was used to explore the association between anti-S-RBD titer and survival. Age, gender, days since symptom onset, immunosuppressive conditions and use of monoclonal Ab (mAb) were explored as possible confounders. Result(s) 534 patients were enrolled. Their mean age was 71 years, 63% were male and 61% vaccinated;42% had >=1 immunosuppressive condition among hematological or solid malignancy, HIV, diabetes, end-stage renal failure, liver cirrhosis, organ transplant or immunosuppressive treatment. Antibody titer was significantly higher among vaccinated than among unvaccinated patients (1166 vs 158 BAU/ml;p< 0.001). Among vaccinated subjects, lower titer of anti-S-RBD were measured among those with hematological malignancies (1282 vs 471 BAU/mL;p< 0.001) or who were receiving immunosuppressive therapy (1287 vs 537 BAU/ml;p< 0.001). Older age, shorter time between onset of symptoms and hospitalization and immunosuppressive conditions were associated with higher rates of death or intubation (Fig 1). Using Cox regression stratified for vaccination, a significant association between anti-S-RBD titer and risk of death/intubation was observed (per log2 BAU/ml increase, HR 0.93;95%CI 0.88-0.99;p=0.020), independently of age (per year increase, HR 1.03;95%CI 1.01-1.04), male gender (HR 1.00;95%CI 0.70-1.42) and presence of immunosuppressive conditions (HR 1.46;95%CI 1.01-2.10). Adjustment for mAb treatment did not change the results to a significant Extent. Conclusion(s) Low anti-S-RBD titer was associated with poor outcome among patients hospitalized for COVID19-related pneumonia, regardless of vaccination. In addition, older age and presence of immunosuppressive conditions remain important predictors of mortality. Kaplan-Meier Curves for intubation-free survival according to age, days from symptoms' onset, presence of immunosuppressive conditions and anti-S-RBD titer. (Figure Presented).