High vs. Standard Dose Influenza Vaccine in Adult SOT Recipients

The influenza virus is a significant cause of morbidity in adult solid organ transplant (SOT) recipients. However, these individuals show a suboptimal response to vaccines including the standard-dose (SD) inactivated influenza vaccine (IIV). Recent studies have investigated two strategies to overcome poor immune responses in SOT recipients: (1) administration of high-dose (HD)-IIV compared to SD-IIV and (2) two doses of SD-IIV compared to one dose of SD-IIV in the same influenza season. The first study compared HD-IIV vs. SD-IIV in adult SOT and noted HD-IIV was safe and reported higher immunogenicity; however, the median post-transplant period was 38 months. In another phase II trial of adult SOT recipients, two doses of SD-IIV a month apart compared to one-dose SD-IIV revealed increased immunogenicity, with a median post-transplantation period of 18 months. Therefore, these studies lack evaluation in the early post-transplantation period in this vulnerable population when influenza disease is most severe. The administration of two-doses of HD-IIV in the same influenza season has also not been studied in SOT recipients. Moreover, the vast majority of SOT influenza vaccinations studies have not substantively evaluated prolonged immunogenicity. Thus, the optimal immunization strategy for SOT recipients less than 12 months post-transplant is poorly-defined. In addition, the immunologic predictors and correlates of influenza vaccine immunogenicity in SOT recipients have not been defined. The investigators hypothesize that adult solid organ transplant recipients that are 1-11 months out from transplant and are receiving high-dose inactivated influenza vaccine will have higher hemagglutination inhibition (HAI) geometric mean titers to influenza A antigens compared to adult SOT recipients receiving standard-dose inactivated influenza vaccine. To test this hypothesis and address the above critical knowledge gaps, The investigators propose to conduct a phase II multicenter randomized controlled trial comparing either two doses HD-IIV, two doses of SD-IIV, or one-dose of HD-IIV in adult kidney, heart, and liver SOT recipients 1-11 months post-transplantation. The results of this study will address significant gaps in knowledge regarding influenza vaccine strategies and immune responses in adult SOT recipients and will guide vaccine recommendations in this vulnerable population.