High Dose Flu Vaccine in Treating Children Who Have Undergone Donor Stem Cell Transplant

1. Inclusion criteria 1. Allogeneic HSCT recipients who are 3-35 months post-transplant; 2. 3-17 years of age, inclusive; 3. Available for duration of study; 4. Patients with stable GVHD for at least 4 weeks will be eligible (stable is defined as having no major increases in systemic immunosuppressive therapy for GVHD; adjustments of established medications to obtain a stable target level are acceptable and do not impact eligibility). Parent/legal guardian willing and capable of signing written informed consent; 5. Parent/legal guardian expected to be available for entire study; 6. Parent/legal guardian can be reached by telephone and/or electronic communication. 7. Subjects must have a platelet count of ≥30,000 to receive the immunizations. Patients requiring platelet transfusions are eligible to enroll and must have a platelet count ≥30,000 within 72 hours prior to their immunization, or platelet count ≥75,000 without transfusion documented within 30 days for subjects \<12 months post-transplant and within 90 days for subjects 12-35 months post-transplant. 2. Exclusion criteria 1. History of hypersensitivity to previous influenza vaccination or severe hypersensitivity to eggs/egg protein; 2. History of Guillain-Barre syndrome; 3. Evidence of hematologic malignancy or disease relapse post-transplant (stable mixed chimerism is permitted); 4. History of receiving current year seasonal influenza vaccine post-transplant; 5. Pregnant female; 6. History of proven influenza disease after September 1, 2018 prior to enrollment 7. Non-allogeneic (e.g. autologous) or syngeneic hematopoietic SCT recipients; 8. History of known active infection with HIV, Hepatitis B or Hepatitis C; 9. History of known severe latex hypersensitivity; 10. Subjects who have received stem cell boost or delayed donor lymphocyte infusion within 90 days prior to enrollment, including day of enrollment; 11. Receipt of IVIG/SCIG \<27 days prior to calendar day of vaccination; 12. Subjects who have participated in year 1 and/or 2 of the study, and received study vaccine Criteria for temporarily delaying vaccine administration: The following conditions are temporary or self-limiting, and a subject may be included in the study once the condition has resolved, provided that the subject is otherwise eligible: 1). Fever ≥100.4ºF/38.0ºC (oral measurement), or an acute illness within 48 hours of enrollment 2). Receipt of any live vaccines within four weeks or any inactivated vaccines within two weeks prior to potential study vaccination. Note: if patients were eligible for vaccine 1, they will be eligible to receive vaccine 2 regardless of any changes on their GVHD status, unless it is deemed not medically safe to receive influenza vaccine. For subjects who were enrolled and vaccinated in 2016-17, 2017-18, or 2018-19, the goal is to enroll individuals who participated in the previous influenza season year and administer the same vaccination as the previous year. These subjects are referred to as repeaters. For example, subjects enrolled in 2016-17 could re-enroll in 2017-18, subjects enrolled in 2017-18 could re-enroll in 2018-19, and subjects in 2018-19 are deemed eligible to re-enroll in 2019-20 as repeaters. Subjects may only enroll as a repeater one time and must enroll the year after their original enrollment. Subjects must receive at least one vaccine to be eligible as a repeater in the subsequent year. Enrollment Criteria for Subjects who Participated in the previous influenza season * Repeaters will retain their original study ID and their randomization number * Previous screen failures will not be enrolled. * If visit 4 from the previous influenza season and visit 1 from the current influenza season year occur on the same day, lab results from visit 4 (prior to consent) can be part of visit 1. 1. Inclusion criteria 1. Available for duration of study; 2. Patients with stable GVHD for at least 4 weeks will be eligible (stable is defined as no major change in systemic immunosuppressive therapy for worsening GVHD; adjustment of actual dose to obtain a stable target level is acceptable). 3. Subjects must have a platelet count of ≥30,000 to receive the immunizations. Patients requiring platelet transfusions are eligible to enroll and must have a platelet count ≥30,000 within 72 hours prior to their immunization, or platelet count ≥75,000 without transfusion documented within 30 days for subjects \<12 months post-transplant and within 90 days for subjects 12-35 months post-transplant. 4. Parent/legal guardian willing and capable of signing written informed consent; 5. Parent/legal guardian expected to be available for entire study; 6. Parent/legal guardian can be reached by telephone and/or electronic communication. 2. Exclusion criteria 1. History of hypersensitivity to previous influenza vaccination or severe hypersensitivity to eggs/egg protein; 2. History of Guillain-Barre syndrome; 3. Evidence of hematologic malignancy or disease relapse post-transplant (stable mixed chimerism is permitted); 4. History of receiving current year seasonal influenza vaccine post-transplant; 5. Pregnant female; 6. History of proven influenza disease after September 1, 2019 but prior to enrollment 7. History of known active infection with HIV, Hepatitis B or Hepatitis C; 8. Subjects who have received stem cell boost or delayed donor lymphocyte infusion within 90 days of enrollment, including day of enrollment 9. Receipt of IVIG/SCIG \<27 days prior to calendar day of vaccination 10. Non-allogeneic (e.g. autologous) or syngeneic hematopoietic SCT recipients; 11. Subjects who have participated in year 1 and/or 2 of the study and received study vaccine. Criteria for temporarily delaying vaccine administration: The following conditions are temporary or self-limiting, and a subject may be included in the study once the condition has resolved, provided that the subject is otherwise eligible: 1). Fever ≥100.4ºF/38.0ºC (oral measurement), or an acute illness within 48 hours of enrollment 2). Receipt of any live vaccines within four weeks or any inactivated vaccines within two weeks prior to potential study vaccination. Note: if patients were eligible for vaccine 1, they will be eligible to receive vaccine 2 regardless of any changes on their GVHD status, unless it is deemed not medically safe to receive influenza vaccine. Note: Previous Screen failures who were not vaccinated can be enrolled and will be assigned the same study ID number. Criteria for temporarily delaying vaccine administration: The following conditions are temporary or self-limiting, and a subject may be included in the study once the condition has resolved, provided that the subject is otherwise eligible: 1). Fever ≥100.4ºF/38.0ºC (oral measurement), or an acute illness within 48 hours of enrollment 2). Receipt of any live vaccines within four weeks or any inactivated vaccines within two weeks of study vaccination.