BNT162b2 or CoronaVac as the Third Dose against Omicron: Neutralizing Antibody Responses Among Transplant Recipients Who Had Received Two Doses of CoronaVac

Abstract Introduction: We evaluated neutralizing antibody and anti-spike antibody (anti-S) response against omicron variant in solid organ (SOT) or hematopoietic stem cell (HSTC) receivers after third dose of BNT162b2 (BNT) or CoronaVac (CV) following two doses of CV. Methods: In total, 95 participants who underwent SOT (n=62; 44 liver, 18 kidney) or HSCT (n=27; 5 allogeneic, 22 autologous) were included from five centers in Turkey. The median time between third doses and serum sampling was 154 days. The vaccine-induced antibody responses of both neutralizing antibodies and Anti-Spike antibodies were assessed by plaque neutralizing assay and immunoassay. Results: Neutralizing antibody and anti-spike IgG levels were significantly higher in transplant patients receiving BNT compared to those receiving CV (GMT:26.76 vs 10.89; p=0.03 and 2116 Au/ml vs 172.1 Au/ml; p<0.001). Solid organ transplantation recipients, particularly liver transplant recipients, showed lower antibody levels than HSCT recipients. Thus, among HSCT recipients, the GMT after BNT was 91.29 and it was 15.81 in the SOT group (p<0.001). In SOT, antibody levels after BNT in kidney transplantation recipients was significantly higher than that in liver transplantation recipients (GMT:48.32 vs 11.72) (p<0.001). Besides, the neutralizing antibody levels after CV were very low (GMT: 10.81) in kidney transplantation recipients and below the detection limit (<10) in liver transplant recipients. There was a weak correlation between the neutralizing and anti-Spike antibody responses (r=0.36). Conclusion: This study highlights the superiority of BNT responses against omicron as a third dose among transplant recipients after two doses of CV. Lack of neutralizing antibody against omicron after CV in liver transplant recipients should be taken into consideration particularly in countries where inactivated vaccines are available in addition to mRNA vaccines.