Value of quantitative SARS-CoV-2 spike antibodies in assessing risk of severe COVID-19: A retrospective cohort study

Since coronavirus disease 2019 (COVID-19) pandemic, its variants have challenged vaccine effectiveness and immunity, particularly among high-risk individuals. Assessment of the risk of severe COVID-19 in these populations is crucial for informed therapeutic decisions. We aim to correlate early quantitative SARS-CoV-2 spike antibody (S ab) levels in SARS-CoV-2 infections with the risk of severe COVID-19.

We conducted a retrospective cohort study of hospitalized patients with early-stage COVID-19 and S ab titers between April 2021 and June 2022. S ab titers were stratified into four categories: <500 units/milliliter (U/mL), 500 to <1500 U/mL, 1500 to <5000 U/mL and ≥5000 U/mL, and their effects on the risk of severe COVID-19 were analyzed. Severe COVID-19 was defined as the development of pneumonia requiring oxygen supplementation, intensive care unit (ICU) admission, or death.

Among the 1665 patients with early-stage COVID-19, 61(3.66 %) developed severe COVID-19. S ab titers were significantly lower in patients who developed severe COVID-19; 72.13 % of these patients had titers below 500 U/mL, whereas 24.19 % of the patients in the non-severe group (P < 0.01) had titers below 500 U/mL during the Delta and Omicron periods. Patients with S ab titers ≥5000 U/mL had an adjusted odds ratio of 0.12 (95 % CI: 0.05-0.33, P < 0.01) for severe COVID-19 compared with those with titers <500 U/mL, independent of vaccination status, variant period, and comorbidities.

S ab titers less than 500 U/mL are associated with an increased risk of severe COVID-19. The quantitative S ab titer may serve as a practical surrogate for SARS-CoV-2 immunity.