28 Humoral response to SARS-CoV-2 vaccination among heart transplant recipients aged 18–70 years of age administered two doses of an adenoviral vector (ChAdOx1 nCoV-19) vaccine and a messenger RNA (BNT162b2) booster

IntroductionSolid-organ transplant (SOT) recipients have an excess mortality risk from severe acute respiratory syndrome coronavirus (SARS-CoV-2), while simultaneously initial reports have suggested blunted responses to messenger RNA (mRNA) vaccination. A paucity of data on adenoviral vector vaccines and heterologous booster use in SOT recipients exists. Hence, we undertook a two-phase study to firstly describe the safety and humoral response to two doses of the adenoviral vector ChAdOx1 nCoV-19 vaccine in our heart transplant population. The second phase sought to examine the humoral response to a heterologous mRNA booster in this patient cohortMethodsHeart transplant recipients aged 18 to 70 years of age were prospectively enrolled in this study. Participants had a serum blood sample drawn after each vaccination dose to test for total antibodies against the receptor-binding domain (RBD) of the spike (S) protein (anti-spike antibodies) using the quantitative Elecsys anti-SARS-CoV-2 S immunoassay. A screening questionnaire complemented with a serum sample testing for anti-nucleocapsid antibodies was employed to detect prior SARS-CoV-2. Participants were excluded if they had a history of SARS-CoV-2 infection or if they contracted the virus during the study period.ResultsA total of 92 heart transplant patients (mean age 50±12 years, 29% female) were enrolled in the first phase of the study. All included patients had a negative anti-nucleocapsid antibody result and no history of SARS-CoV-2. At a mean of 12±2 weeks after the initial ChAdOx1 nCoV-19 vaccine 24% of patients (n=22) had a detectable antibody response, increasing significantly to 34.8% (n=32) 29 (IQR 28–31) days following dose 2, (p