Short-Term Immune Response After Inactivated SARS-CoV-2 (CoronaVac, Sinovac) And ChAdOx1 nCoV-19 (Vaxzevria, Oxford-AstraZeneca) Vaccinations in Thai Health Care Workers

Background: Inactivated SARS-CoV-2 (CoronaVac,Sinovac, or SV) and ChAdOx1 nCoV-19 (Vaxzevria,Oxford-Astra Zeneca, or AZ) vaccines have been administered to the health care workers (HCWs) in Thailand. Objective: To determine the short-term immune response after the SV and AZ vaccinations in HCWs. Methods: In this prospective cohort study, HCWs who completed a 2-dose regimen of the SV or AZ were included. Immune response was evaluated by surrogate viral neutralization test (sVNT) and anti-SARS-CoV-2 total antibody. Blood samples were analyzed at 4 and 12 weeks after the complete SV vaccination and at 4 weeks after each dose of the AZ vaccination. The primary outcome was the seroconversion rate at 4-weeks after complete immunization. Results: Overall, 185 HCWs with a median (IQR) age of 40.5(30.3-55.8) years (94 HCWs in the SV group and 91 in the AZ group) were included. At 4 weeks after completing the SV vaccination, 60.6% (95%CI:50.0-70.6%) had seroconversion evaluated by sVNT(≥68%inhibition), comparable to the patients recovered from mild COVID-19 infection(69.0%), with a rapid reduction to 12.2%(95%CI:6.3-20.8) at 12 weeks. In contrast, 85.7%(95%CI:76.8-92.2%) HCWs who completed the second dose of the AZ for 4 weeks had seroconversion, comparable to the COVID-19 pneumonia patients(92.5%). When using the anti-SAR-CoV-2 total antibody level(≥132 U/ml) criteria, only 71.3% HCWs in the SV group had seroconversion, compared to 100% in the AZ group. Conclusion: A rapid decline of short-term immune response in the HCWs after the SV vaccination indicates the need for a vaccine booster, particularly during the ongoing spreading of the SAR-CoV-2 variants of concern.