ABSTRACT
Background: Inactivated SARS-CoV-2 vaccine (CoronaVac) is commonly used in national immunization programmes. However, an immune response of CoronaVac significantly declined after 3 months, our study, thus, aimed to explore the immune response against COVID-19 following the booster dose by assessing both B-cell and T-cell activities compared to the convalescent samples. Methods: In this prospective cohort study, 98 healthcare workers with a 2-dose CoronaVac vaccination with a subsequent booster dose of ChAdOx1 nCoV-19 (n=56) or BNT162b2 (n=42) were included during March and October 2021. Immune responses were evaluated by surrogated viral neutralization test (sVNT, cPass™), anti-SARS-CoV-2 RBD total antibodies (Elecsys®) and the ELISPOT with spike (S1) peptide pools. The samples were analyzed at baseline, 4 and 12 weeks after the second CoronaVac and 4 weeks after a booster dose. In addition, convalescent sera and peripheral blood mononuclear cells (PBMCs) of the COVID-19 patients were collected at 4 weeks after diagnosis. Results: Median (interquartile range, IQR) age was 40 (31-52) years old with female predominant (80%). The median (IQR) interval after the second CoronaVac was 88 (74-92) days for ChAdOx1 nCoV-19 and 113 (112-115) days for BNT162b2. There was a significant decrease in neutralizing antibodies at the 12th week after primary CoronaVac vaccination (Figure 1). At 4 weeks after the ChAdOx1 nCoV-19 booster, median (IQR) level of sVNT and anti-RBD total antibody levels were 98.1% (97.9-98.2%) and 7768 (5349-11142), respectively, which were significantly different from the BNT162b2 booster, 98.5% (98.5-98.6%) and 25129 (17531-39434) BAU/mL, respectively (p<0.001 both). The antibody levels of the booster vaccine group were significantly higher than in the COVID-19 patients, which median (IQR) of sVNT was 80.8% (61.7-94.2%) in the mild COVID-19 and 93.8% (85.4-95.6%) in COVID-19 pneumonia, while anti-RBD total antibody levels were 94 (22-207) and 222 (130-378) BAU/mL, respectively. Using the ELISPOT with S1 peptide pools, median (IQR) of T cell response was 106 (24-256) and 196 (60-244) Spot Forming Unit (SFU)/millions of PBMCs for ChAdOx1 nCoV-19 and BNT162b2, respectively (p 0.49) which were comparable to the COVID-19 cases. Conclusion: A 2-dose CoronaVac followed by ChAdOx1 nCoV-19 or BNT162b2 effectively boosted a significantly higher antibody response than the natural COVID-19 infection. In addition, BNT162b2 booster induced significantly higher antibody levels than ChAdOx1 nCoV-19.