SARS-CoV-2 Vaccination-Induced Immunogenicity in Heart Transplant Recipients

SARS-CoV-2 vaccine-elicited immune responses in solid organ transplant recipients

Solid organ transplant recipients (SOTRs) are considered a high-risk group for coronavirus disease 2019 (COVID-19). The adaptive immune responses generated by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination include humoral and cellular immune responses. Most studies on the SARS-CoV-2 vaccine have focused primarily on humoral immunity, but cellular immunity is vital for effectively controlling progression to severe COVID-19. In SOTRs, the vaccine-induced adaptive immune response is significantly attenuated compared to the response in healthy individuals. Nevertheless, vaccinated SOTRs exhibit a reduced rate and severity of SARS-CoV-2 infection. This review aims to provide a concise overview of the current understanding of SARS-CoV-2 vaccine-induced immune responses in SOTRs.

Epidemiological and Clinical Characteristics of the Course of COVID-19 Among Vaccinated and Unvaccinated Heart Transplant Recipients in Slovenia

Background: Patients receiving heart transplantation require lifelong immunosuppression and compared to the general population, they have a more than five times higher chance of acquiring COVID-19, and their mortality rates are higher. The aim of the present study was to estimate the epidemiological and clinical characteristics of COVID-19 in heart transplant recipients (HTRs) in Slovenia to estimate the vaccination rate and evaluate possible vaccination-hesitant subgroups. Methods: All SARS-CoV-2-positive HTRs (N = 79) between 1 March 2020 and 31 December 2023 at the Infectious Diseases Department, University Medical Centre Ljubljana, Slovenia, were included retrospectively. Demographic, clinical and vaccination data were extracted from medical documentation and a statistical evaluation was performed. Results: The observed vaccination rate was 63.3%, but among patients who received transplants before the pandemic, it was statistically significantly higher (p = 0.027). Vaccinated HTRs were statistically significantly older (p = 0.004) and had a significantly higher Charlson Comorbidity Index (p = 0.018). Our results indicate no significant differences between vaccinated and unvaccinated HTRs regarding acute respiratory insufficiency (p = 0.135), length of hospital stay (p = 0.106), intensive care unit admission (0.414) and in-hospital mortality (p = 0.317), but we observed statistically more frequently an asymptomatic course in those vaccinated (p = 0.050), and a longer length of stay in vector vaccine recipients (p = 0.011) and in those not re-vaccinated (p = 0.030). There was a significantly higher re-vaccination rate in males (p = 0.005). Conclusions: An asymptomatic course of COVID-19 was more often observed in vaccinated HTRs. Our findings suggest statistically significant differences in COVID-19 vaccine acceptance rates; younger HTRs and those transplanted after the pandemic are more hesitant to vaccinate, while females accept booster doses less frequently.

Measures to Increase Immunogenicity of SARS-CoV-2 Vaccines in Solid Organ Transplant Recipients: A Narrative Review

Purpose of review: To review the data on the immunogenicity of COVID-19 vaccines, administered by different strategies, in solid organ transplant recipients (SOTRs). Recent findings: COVID-19 booster vaccines were given to SOTRs as a widespread practice in many transplant centers, mostly as the third and/or fourth dose in an extended vaccine series, with a significantly improved humoral response compared with the initial two-dose scheme. However, one-third of SOTRs remained unresponsive, despite these boosters. Next steps: Vaccination with standard dosing remains the most feasible strategy for attaining protection against COVID-19. Additional booster doses and temporarily holding or reducing mycophenolate mofetil/mycophenolic acid may provide immunogenicity to vaccines, according to recent studies demonstrating some efficacy with these measures. Preexposure prophylaxis with monoclonal antibodies showed benefit in immunocompromised patients but is no longer recommended by the National Institutes of Health (NIH) due to diminished efficacy against Omicron and recent variants. Screening for the presence and titers of SARS-CoV-2-specific antibodies in SOTRs is not recommended in most clinical settings. T cell-based techniques are needed to evaluate vaccine efficacy and risk of infection. As SARS-CoV-2 continues to evolve, new vaccines based on conservative protein component/complexes of the COVID virus, in addition to its spike protein, are warranted to offer prolonged protection.