Exposure factors associated with SARS-CoV-2 seropositivity are not predictive for higher humoral immune responses: A cross-sectional cohort study in the general population

Introduction: Higher antibody levels, in particular antibodies directed against the receptor-binding domain (RBD) of the spike protein, protect against re-infection with SARS-CoV-2. Quantitative antibody response data provide insight into population immunity and are essential for decision-making on booster-vaccination strategies. We aimed to identify predictors for higher antibody responses such as gender, age, experienced COVID-19-compatible symptoms, disease severity and exposure to pre-determined risk factors associated with SARS-CoV-2 seropositivity. Materials and methods: Quantitative anti-S-RBD responses were analysed in seropositive vaccine-naive individuals (n = 1,857) from a study population of 10,001 adults, including healthcare workers (n = 211) and individuals with a known date of a positive PCR (n = 214). Regression models tested associations between age, gender, the period of symptoms, disease severity, pre-identified exposure factors associated with SARS-CoV-2 seropositivity, and anti-S-RBD responses. Results: Symptoms of more severe disease (fever and/or dyspnoea: OR 2.42 [95%CI 1.76–3.34], and hospital admission: OR 11.41 [95%CI 4.66–27.97]), and a longer interval between COVID-19-compatible symptoms and serum collection (OR 3.17 [95%CI 1.32–7.63]) were predictive for anti-S-RBD levels =300 U/mL. Working in healthcare was inversely associated with anti-S-RBD levels =300 U/mL (OR 0.51 [95%CI 0.31–0.82]). None of the pre-identified exposure factors associated with SARS-CoV-2 seropositivity could be identified as predictive of higher anti-S-RBD responses. Conclusion: No exposure factors were identified as predictors of higher neutralising antibody responses. Nevertheless, higher neutralising antibody levels in individuals with more severe symptoms suggest better immunological protection against SARS-CoV-2 re-infection. In seroprevalence studies, that mainly include asymptomatic or mildly infected individuals, the determination of quantitative antibody responses may help in the interpretation of population immunity.