Comparing Results of Five SARS-CoV-2 Antibody Assays Before and After the First Dose of ChAdOx1 nCoV-19 Vaccine among Health Care Workers.

Reliable results of serologic positivity of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody before and after AstraZeneca (AZ) vaccination are essential to estimate the efficacy of vaccination. We assessed the positivity rates and associated factors using five SARS-CoV-2 antibody assays. A total of 228 paired serum samples (456 samples) were obtained from 228 participants. After baseline sampling, the second sampling was conducted between 11-28 days after the first dose of AZ. Sera were tested using five SARS-CoV-2 antibody assays, including two surrogate virus neutralization tests. A questionnaire on symptom, severity, and duration of adverse reactions was completed by all participants. The overall positive rates for SARS-CoV-2 antibody were 84.6% for Roche, 92.5% for Abbott, 75.4% for Siemens, 90.7% for SD Biosensor, and 66.2% for GenScript assays after the first dose of AZ vaccination. The positive rates and antibody titer of sera obtained between 21-28 days were significantly higher than those obtained between 11-20 days in all five assays. More severe and longer duration of adverse reactions were related to higher SARS-CoV-2 antibody levels. The agreements and correlations among the applied assays were substantial (к=0.73-0.95) and strong (ρ=0.83-0.91). A single dose of AZ vaccination led to high positivity rates based on the five assays. Days after vaccination and adverse reactions could help estimate serologic conversions. The results should be interpreted cautiously considering the applied assays and cutoffs. Our findings could inform decisions regarding vaccination and laboratory settings and, thus, contribute to the control of the spread of SARS-CoV-2 infection.