BACKGROUND: Omicron variant viruses spread rapidly, even in individuals with high vaccination rates. This study aimed to determine the utility of the antibody against the spike protein level as a predictor of the disease course of COVID-19 in vaccinated patients. METHODS: Between 11 December 2021 and 10 February 2022, we performed a prospective observational cohort study in South Korea, which included patients infected with delta –and –omicron variants. Multivariable logistic regression analysis to determine the association between antibody levels and the outcomes was conducted.The relationship between antibody levels and cycle threshold (Ct) values was confirmed using a generalised linear model. RESULTS: From 106 vaccinated patients (39 delta and 67 omicron), the geometric mean titres of antibodies in patients withfever (≥37.5 °C), hypoxia (≤94% of SpO(2)), pneumonia, C-reactive protein (CRP) elevation (>8 mg/L), or lymphopenia (<1,100 cells/μL) were 1,201.5 U/mL, 98.8 U/mL, 774.1 U/mL, 1,335.1 U/mL, and 1,032.2 U/mL, respectively. Increased antibody levels were associated with a decrease in the fever occurrence (adjusted odds ratio [aOR], 0.23; 95% confidence interval [CI], 0.12–0.51), hypoxia (aOR, 0.23; 95% CI, 0.08–0.7), CRP elevation (aOR, 0.52; 95% CI, 0.29–0.0.94), and lymphopenia (aOR, 0.57; 95% CI, 0.33–0.98). Ct values showed a positive correlation between antibody levels (P =0.02). CONCLUSION: Antibody levels are predictive of the clinical course of COVID-19 in vaccinated patients with delta and omicron variant infections. Our data highlight the need for concentrated efforts to monitor patients with SARS-CoV-2 infection who are at risk of low antibody levels.
Antibody level predicts the clinical course of breakthrough infection of COVID-19 caused by delta and omicron variants: a prospective cross-sectional study