SARS-CoV-2 specific antibody responses in healthcare workers after a third booster dose of CoronaVac or BNT162b2 vaccine

The first SARS-CoV-2 vaccination campaign in Turkey has started in mid-January for the healthcare workers (HCWs) with the inactive virus vaccine CoronaVac (Sinovac). After four and a half months, the Turkish Ministry of Health rolled out a booster-dose vaccination campaign for HCWs and all people over 50 years old beginning in July 2021. The individuals eligible were given the choice of either CoronaVac or mRNA vaccine BNT162b2 for the third booster-dose vaccination. This study aimed to evaluate SARS-CoV-2 IgG antibody titers against the S1 subunit of the spike protein as a marker of the humoral response in 179 HCWs who received a third booster dose of either CoronaVac or BNT162b2. A total of 136 HCWs, 71 female (52.2%) and 65 male (47.8%), completed both serum collections on Days 0 and 28. The median SARS-CoV-2 IgG S Protein (SP) titer in all participants before the vaccination was 175.7 AU/ml. Of 136 HCWs, 103 (75.73%) chose BNT162b2 vaccine and 33 (24.26%) chose CoronaVac as the third booster dose. There was a significant difference between the BNT162b2 group and the CoronaVac group in terms of SARS-CoV-2 IgG SP titers (p < 0.001). The median SARS-CoV-2 IgG SP titers in BNT162b2 group (n = 103) and in CoronaVac group (n = 33) were 17619.3 AU/ml and 1153.0 AU/ml, respectively. The third booster dose with BNT162b2 and CoronaVac increased antibody titers in each participant a mean of 162-fold and 9-fold, respectively. HCWs in the BNT162b2 group reported more frequent adverse events than HCWs in the CoronaVac group (p < 0.001).