Comparing Five SARS-CoV-2 Antibody Assay Results Before and After the First and Second ChAdOx1 nCoV-19 Vaccination Among Health Care Workers: A Prospective Multicenter Study.

Jeong, Seri; Lee, Nuri; Lee, Su Kyung; Cho, Eun-Jung; Hyun, Jungwon; Park, Min-Jeong; Song, Wonkeun; Jung, Eun Ju; Woo, Heungjeong; Seo, Yu Bin; Park, Jin Ju; Kim, Hyun Soo

Reliable results for serologic positivity to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody after the second dose of AstraZeneca (AZ) vaccination are important to estimate the real efficacy of vaccination. We evaluated the positivity rates and the changes of semi-quantitative antibody titers before and after the first and second ChAdOx1 nCoV-19 Vaccinations using five SARS-CoV-2 antibody assays, including two surrogate virus neutralization tests. A total of 674 serum samples were obtained from 228 participants during three blood sampling periods. A questionnaire on symptoms, severity and adverse reactions duration was completed after the second vaccination. The overall positive rates for all assays were 0.0-0.9% before vaccination, 66.2-92.5% after the first vaccination, and 98.2-100.0% after the second vaccination. Median antibody titers in five assays after the second dose of vaccination were increased compared to those after the first dose (106.4-fold increase for Roche total antibody, 3.6-fold for Abbott IgG, 3.6-fold for Siemens, 1.2-fold for SD Biosensor V1 neutralizing antibody, and 2.2-fold for GenScript neutralizing antibody). Adverse reactions reduced after the second dose in 89.9% of participants compared to after the first dose. Overall, the second vaccination led to almost 100% positivity rates based on these SARS-CoV-2 antibody assays. The results should be interpreted with caution, considering the characteristics of applied assays. Our findings could inform decisions regarding vaccination and the use of immunoassays, thus, contributing to the SARS-CoV-2 pandemic control.