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RESEARCH PRODUCT

Antibodies Responses to SARS-CoV-2 in a Large Cohort of Vaccinated Subjects and Seropositive Patients

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Background: COVID-19 is a current global threat and characterisation of antibody response to SARS-CoV-2 is vitally important to update vaccine development and strategies. Methods: In this study we assessed SARS-CoV-2 antibody concentrations in SARS-CoV-2 positive patients (N=272) and subjects vaccinated with BNT162b2 m-RNA Covid-19 vaccine (N=1,256). For each participant socio-demographic data, COVID-19 vaccination records, serological analyses and SARS-CoV-2 infection status have been collected. IgM and IgG antibodies against S1/S2 antigens of SARS-CoV-2 were detected. Findings: Almost all vaccinated subjects (99·8%) showed a seropositivity to anti-SARS-COV-2 IgG and more than 80% vaccinated subjects had IgG concentrations >200 AU/mL. SARS-CoV-2 subjects had IgG concentrations <100 AU/mL and these concentrations were statistically significantly lower than in vaccinated individuals (p<0·001).The observed difference has been confirmed by multivariable analyses, suggesting that vaccination confers higher IgG concentrations than natural infection. Older age and days after immunization, instead, have been found to be associated with a statistically significant decrease in the probability of having high antibody titres. Interpretation: Our findings could support the vaccination campaigns confirming the high immunogenicity of the SARS-CoV-2 vaccine under investigation also with respect to the natural infection. Further studies will be required for evaluating the role of age and days after immunization in the persistence of vaccine antibodies and protection from the disease. Funding Statement: None to declare. Declaration of Interests: None to declare. Ethics Approval Statement: The study has been approved by the Ethical Committee of the A.O.U.P. “P. Giaccone” on June 24th, 2020, protocol number 0006.