Humoral response to heterologous prime-booster vaccination in heart transplant recipients aged 18-70 years primed with a viral vector SARS-CoV-2 vaccine

Abstract

Solid organ transplant recipients have demonstrated a blunted immune response to standard 2-dose vaccination against SARS-CoV-2. This study sought to determine the humoral response to heterologous booster vaccination (viral vector vaccine dose 1 and 2 + mRNA booster). Heart transplant recipients, aged 18 to 70 years of age who initially received two doses of the viral vector ChAdOx1 nCoV-19 vaccine followed by a BNT162b2 mRNA booster were recruited. A detectable antibody response in the absence of prior SARS-CoV-2 was the primary outcome measured. This was defined as an anti-spike titre of ≥0.8 U/mL on the Elecsys anti-SARS-CoV-2 S immunoassay. A total of 80 heart transplant patients (mean age 49 ± 13 years, 28% female) were included. Blood samples were drawn at a median of 30 (IQR 28-33) days after the BNT162b2 mRNA booster. The frequency of a detectable antibody response increased from 37.5% (n = 30) after dose 2 to 56% (n = 45) post dose 3 (p < 0.001). A non-detectable antibody response was significantly more common in recipients with a shorter time interval from transplantation (p < 0.001), lower likelihood of cardiac allograft vasculopathy (p = 0.003) and in those prescribed a triple versus dual immunosuppressant regime (p = 0.009) and a tacrolimus versus cyclosporine basedregimen (p = 0.007). Despite heterologous prime-booster vaccination 44% of this vulnerable population ultimately continue to have no detectable antibodies.

Keywords: SARS-CoV-2; heart transplant; heterologous prime-booster vaccination; humoral response.

FIGURE 1

(A) Frequency of a detectable antibody response after each vaccination for 80 heart transplant recipients. (B) Interval change in anti‐spike antibody titres between the 2nd ChAdOx1 nCoV‐19 vaccine and the 3rd dose mRNA (BNT162b2) booster vaccine. Note: each frequency represents more than one person. Dotted line = threshold for detectable antibody response to SARS‐C0V‐2 vaccination (≥0.8 U/ml)