B-091 Assessing Postvaccination SARS-CoV-2 Neutralizing Antibodies at Different Timepoints: a Laboratory-Based Study

Abstract

Abstract Background Serum-neutralizing antibodies (NAbs) against SARS-CoV-2 may be produced as a result of either viral infection or vaccination. NAbs can disrupt the connection between the RBD (Receptor-Binding Domain) of the Spike protein and the ACE2 receptor, hindering the virus's entry into cells. However, only a portion of these antibodies are able to neutralize the virus and prevent it from infecting new cells. While the presence of NAbs should not be considered a guarantee of neither immunity nor vaccine effectiveness, it can serve as an indicator for seroprevalence studies in healthcare settings. The purpose of this study was to compare results for NAbs from a group of healthcare individuals that received either CoronaVac/Sinovac (CVC/S) or Oxford-AstraZeneca (O/AZ) in São Paulo, Brazil. Methods Study Population and Characteristics: The current study evaluated a total of 33 and 34 healthcare professionals that received, respectively, O/AZ and CVC/S in the year 2021. Blood samples were collected 15 days (15D1) after the first dose of vaccination and at 30 (30D2), 60 (60D2), or 90 (90D2) days after the second dose. The presence of neutralizing antibodies was assessed with the cPassTM SARS-CoV-2 Neutralization Antibody Detection Kit GenScript. Results were classified into three categories based on reference values: not reactive (0–20%), undetermined (20–30%), and reactive (greater than 30%). Results Among the 67 health professionals, mostly were women in both vaccination groups: CVC/S (85.3%) and O/AZ (90%). At 15 days after receiving the first dose, the presence of neutralizing antibodies was detected in individuals who received both vaccines. However, a total of 32.3% (11/34) and 15.1% (5/33) individuals for CVC/S or O/AZ respectively do not show reactive antibodies at this first period evaluated. NAbs values obtained at 15D1, 30D2, 60D2, and 90D2 for CVC/S and O/AZ were 53.9%, 79.3%, 74.7%, 66.7% (for CVC/S) and 68.2%, 87.7%, 82.9%, 69.6% (for O/AZ). For both vaccination groups, higher levels for neutralizing antibodies were detected at 30 days after the second dose, and decreased at 60 and 90 days. Conclusion Oxford-AstraZeneca induced higher levels of neutralizing antibodies in this group of healthcare individuals. Serum follow-up samples taken at 30D2 elicited increased NAbs compared to other timepoints.