Abstract
Adverse events following vaccination with the ChAdOx1 COVID-19 vaccine may be associated with the titer of neutralizing antibodies (NAbs) against SARS-CoV-2. In this cross-sectional study, a total of 82 HCWs who received the ChAdOx1 COVID-19 vaccine and did not have previous COVID-19 history were enrolled during March 2021. Blood samples were collected from HCWs 3 weeks after the first and second doses of vaccine, and NAbs were estimated using two types of commercially available kits, the cPass™ SARS-CoV-2 NAbs Kit (Genscript Biotech, Piscataway, NJ, USA) and R-FIND SARS-CoV-2 NAbs ELISA (SG Medical, Seoul, Korea). Median percent signal inhibition of NAbs was significantly higher after the second than after the first dose of vaccine, as determined using both the Genscript (median 43.1[IQR 71.2] vs. 93.6[83.1], p = 0.004) and R-FIND (53.2[82.6] vs. 76.8 [90.6], p = 0.03) kits. The percent signal inhibition of NAbs after the second dose of vaccine was higher in HCWs with than without systemic adverse events after the second dose, as determined using both the Genscript (p = 0.03) and R-FIND (p = 0.07) kits. The two doses of the ChAdOx1 vaccine induced high value of NAbs 3 weeks after vaccination. Immune responses were stronger in HCWs with than without adverse reactions after the second dose of ChAdOx1 vaccine.