Humoral Response to SARS-CoV-2 mRNA Vaccine in Heart Transplant Recipients up to 4 Months After the Third Vaccine Injection

PURPOSE: Recent studies reported poor to moderate humoral response after 2 vaccine doses in heart transplant recipients (HTR). Currently, French authorities recommend 2 and 3 vaccine injections for transplant recipients with and without prior SARS-CoV-2 infection, respectively. This study aimed to evaluate level and durability of humoral immunity with this vaccination strategy. METHODS: This single-center cohort study included HTR followed at Paris Bichat hospital between January 2020 and September 2021. Analyses were performed using automated immunoassays (Abbot) to quantify anti-spike IgG (cut-off ≥ 7.1 BAU/mL) and anti-nucleocapsid IgG (cut-off index > 0.49). Categorical variables were described as number (%) and continuous variables with median (IQR). RESULTS: A total of 181 HTR (75.7% males, age 58 y [47-66]) transplanted between June 1990 and June 2021 were included. Median time from transplantation to first vaccine dose was 4.2 y [1.8-6.6]. 143 HTR (79%) had no SARS-CoV-2 infection history (HTRn) and 38 (21%) contracted the infection (HTRi) (56% before and 42% after vaccination initiation). After 2 vaccine doses, anti-S IgG seroconversion was observed for only 16% (n=12/76) of HTRn. Overall, anti-S IgG titers were lower in HTRn than in HTRi (0.5 [0.2-2.6] vs 578 [1.4-4449] BAU/mL, respectively, p=0.0001). The 3(rd) vaccine dose enabled to obtain 42% (n=33/72) of seroconversion among HTRn with median anti-S titers of 3.2 BAU/mL [0.4-35.0]. Only half seroconverters HTRn reached the 260 BAU/mL cut-off chosen by French authorities to define vaccination efficacy. Interestingly, these patients seem to have a sustained humoral response 4 months after the 3(rd) dose. CONCLUSION: This study gives new insights on the effect of the 3(rd) vaccine dose in HTR with low rate of seroconversion and low titers of anti-S IgG but sustained humoral response when seroconversion occurs. Studies on vaccine efficacy against SARS-CoV-2 variants and cell-mediated immune response in this cohort are ongoing.