(8) 5th Dose Bivalent Omicron-Containing Booster Vaccine Against Covid-19 in Heart Transplant Recipients

PURPOSE: In 2022, omicron (BA.1) and omicron subvariants (BA.2, BA.4, and BA.5), the most antigenically divergent variants to date, outcompeted previous variants in the context of substantial preexisting population immunity from vaccination, infection, or both. Omicron variants continue to cause substantial numbers of illnesses and deaths. Booster immunization with mRNA vaccines improves neutralizing antibody responses against variants and vaccine effectiveness in heart transplant recipients (HTxRx). Nonetheless, the vaccine effectiveness against omicron is lower than that against other variants. The bivalent vaccine contains two mRNA components of SARS-CoV-2 virus, one of the original strain of SARS-CoV-2 and the other one in common between the BA.4 and BA.5 lineages of the omicron variant. This study aims to evaluate the immunogenicity, safety and reactogenicity of omicron-containing bivalent Pfizer-BioNTech COVID-19 booster in HTxRx. METHODS: HTxRx who had received a homologous 2-doses primary/1-2 booster doses BNT162b2 vaccination schedule or 2-/3-/4- doses vaccinated HTxRx with breakthrough infections are prospectively enrolled to receive the bivalent Pfizer-BioNTech COVID-19 booster. Safety assessments include solicited local and systemic adverse reactions within 7 days after bivalent booster administration. Serum samples, collected longitudinally immediately before and 3 weeks after the bivalent booster dose, are tested for SARS-CoV-2 anti-RBD IgG antibodies and for neutralizing antibodies (using live virus micro-neutralization assays) against wild-type (B.1.1.50), the delta variant (B.1.617.2) and four omicron variants (BA.1, BA.2, BA.4 and BA.5). SARS-CoV-2-specific-T-cell response are evaluated in a subset of patients by IFN-γ release of stimulated peripheral blood mononuclear cells. ENDPOINTS: 1) Tolerability and reactogenicity; 2) bivalent booster-induced anti-RBD IgG antibodies; 3) bivalent booster-induced variant-specific neutralizing antibodies; 3) SARS-CoV-2-specific-T-cell response, and 4) post-bivalent booster vaccine infection and hospitalization.