SARS-CoV-2 vaccination in heart transplantation: What we do and do not know

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.

The 90-Day Risk of Hospitalization in Heart Transplant Recipients After COVID-19 Infection

BACKGROUND

Heart transplant recipients are at a high-risk of complications from the coronavirus-2019 (COVID-19) infection. Heart transplant recipients are a special group of persistently immunosuppressed people, and COVID-19 may cause them to experience an unpredictable course of infection, with a risk of hospitalization occurring well beyond their initial infection period. The seriousness of COVID-19 disease in heart transplant recipients emphasizes how vital it is to refer patients promptly and early to specialized heart transplant centers.

METHODS

We retrospectively reviewed all heart transplant recipients at a single center between March 2019 and October 2021. All recipients with positive nasopharyngeal reverse transcriptase-polymerase chain reaction tests for COVID-19 were included in this study. After IRB approval, we obtained medical records and patient data from electronic medical records.

RESULTS

This study followed 126 heart transplant patients from March 2019 to October 2021 of which only 49 had COVID-19 infections. The median age at infection was 58 years (49-65), with 41% female. Race distribution was as follows: 59% Caucasian and 39% African American. The median time from transplant to infection was 384 days (237-677). All infected patients had a 50% dose reduction in mycophenolate mofetil per institutional protocol. The majority of symptoms were cough, fatigue, shortness of breath, and fever. Among all patients with COVID-19, 45 (92%) were vaccinated. Of those vaccinated, 27 (60%) patients received Pfizer initial and booster doses, whereas 18 (40%) received Moderna initial and booster doses. Twelve patients (24%) were hospitalized within 90 days of infection, with only two requiring ICU level of care. The median duration of hospitalization was 5 days (4-9). Of the hospitalized patients, 11 (92%) were discharged, and 1 (8%) died in the hospital. Three of the four unvaccinated patients were hospitalized, and one died while hospitalized. The remaining 37 patients were managed as outpatients.

CONCLUSION

Heart transplant recipients have an increased risk of contracting COVID-19 and developing severe symptoms due to multiple healthcare contacts, preexisting health conditions, and weakened immune systems. Our data highlight that most vaccinated patients do not require hospitalization within 90 days of infection, and those hospitalized have a high likelihood of survival without needing ICU care.

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.

BNT162b2-vaccine-induced neutralization responses are immune correlates of clinical protection against SARS-CoV-2 in heart transplant recipients

BACKGROUND

Defining immune correlates of protection against COVID-19 is pivotal for optimizing the use of COVID-19 vaccines, predicting the impact of novel variants on clinical outcomes, and advancing the development of immunotherapies and next-generation vaccines. We aimed to identify vaccine-induced immune correlates of protection against COVID-19-related hospitalizations in a highly vaccinated heart transplant (HT) cohort.

METHODS

In a case-control study of HT recipients vaccinated with the BNT162b2 vaccine, patients were prospectively assessed for vaccine-induced neutralization of the wild-type virus, and the Delta and Omicron BA.1, BA.2, BA.4, and BA.5 variants. Comparative analyses with controls were conducted to identify correlates of protection against COVID-19 hospitalization. ROC analyses were performed. Primary outcomes were COVID-19 hospitalizations and severity of SARS-CoV-2 breakthrough infection.

RESULTS

The study cohort comprised 59 HT recipients aged 58 (49,65) years with breakthrough infections after three or four monovalent BNT162b2 doses; 41 (69.5%) were men. Thirty-six (61%) patients with COVID-19 were hospitalized; most cases were non-severe (58, 98%). For hospitalized (vs. non-hospitalized) COVID-19 patients, vaccine-induced neutralization titers were significantly lower against all SARS-CoV-2 variants (p < .005). Vaccine-induced neutralization of the wild-type virus and delta and omicron BA.1, BA.2, BA.4, and BA.5 variants was associated with a reduced risk for COVID-19-related hospitalization. The optimal neutralization titer thresholds that were predictive of COVID-19 hospitalizations were 96 (wild-type), 48 (delta), 12 (BA.1), 96 (BA.2), 96 (BA.4), and 48 (BA.5).

CONCLUSIONS

BNT162b2-vaccine-induced neutralization responses are immune correlates of protection and confer clinical protection against COVID-19 hospitalizations.

The COVID-19 Pandemic and Adult Cardiac Transplantation: Impact, Interventions, and Implications

In this review, we provide a comprehensive overview of the impact of the COVID-19 pandemic on adult heart transplantation. We highlight the decline in the number of adult transplantations performed throughout the pandemic as a consequence of restrictions imposed on individual programs and hospitals. There were challenges to maintaining cardiac transplant activity at multiple levels, including organ donation in intensive care units, logistical difficulties with organ procurement, and rapidly changing resource considerations at health system and jurisdictional levels. We also review the impact of COVID-19 on cardiac transplant recipients. Despite the high rates of morbidity and mortality observed during the initial phases of the pandemic among heart transplant patients infected with COVID-19, the availability of effective vaccines, pre-exposure prophylaxis, and specific antiviral therapies have drastically improved outcomes over time. Vaccines have proven to be safe and effective in reducing infections and illness severity, but specific considerations in the immunocompromised solid organ transplant population apply, including the need for additional booster doses to achieve sufficient immunisation. We further outline the strong rationale for vaccination before transplantation wherever possible. Finally, the COVID-19 response created a number of barriers to safe and efficient post-transplantation care. Given the need for frequent evaluation and monitoring, especially in the first several months after cardiac transplantation, the pandemic provided the impetus to improve virtual care delivery and explore noninvasive rejection surveillance through gene expression profiling. We hope that lessons learned will allow us to prepare and pivot effectively during future pandemics and health care emergencies.