Adjuvant, non-live RSV vaccine will be administered to adult lung and allogeneic hematopoietic stem cell transplant recipients. The safety and immunogenicity of this intervention will be studied. Blood work will be collected before and after the intervention, to assess humoral and cellular immunity. Participants will be followed for adverse reaction, hospitalization, RSV breakthrough infection, graft rejection or graft versus host disease. This study has Health Canada and UHN REB approval.

This is a single-arm, open-label, investigational and interventional study to determine the immunogenicity of one dose of RSV vaccine in adult Allogeneic Stem Cell Transplant (alloSCT) or lung transplant (LT) recipients.Patients at least 18 years of age will receive a single dose of adjuvanted RSV vaccine (RSVPreF3, Arexvy, GSK). This vaccine is currently approved in Canada for adults over 60 years of age. Therefore, administration to adult transplant recipients between the age of 18 and 60 years of age is considered off-label. We have ethics approval to conduct this study from UHN and a No Objection Letter from Health Canada.

Study investigators (physicians) will perform the vaccination at hospital outpatient clinics.

Whole blood (total 30mL or 3 tubes) will be collected prior to vaccination and then at 4 weeks, 6 months and 12 months post-vaccination for humoral and cell-mediated immunity assessment. At each time point, 1 red-top blood tube (6mls) for serum and 2 green-top sodium heparin (9mls) blood tubes for plasma and peripheral blood mononuclear cells (PBMCs) will be collected.

Eligible patients will be screened as per the inclusion and exclusion criteria detailed in the screening log. After written informed consent and enrolment, the patient will be allocated a study code and data will be collected for demographics, including age, sex, gender identity, race, language spoken at home, immunosuppression at time of vaccination, time from transplant, immunosuppression regimen at time of transplant, underlying disease, recent lymphocyte count and immunoglobulin levels at the time of vaccination and follow up blood work. For alloSCT recipients, treatment history for Graft versus Host Disease (GvHD) and underlying disease status will be collected. For LT recipients, information regarding recent lung function and rejection episode(s) will be collected. Patients will be contacted at 6 weeks post-vaccination to determine the rates of adverse events including hospitalizations, cardiac, or neurologic events. Patients will then be contacted at 12 months and interviewed to determine whether they had a diagnosis of RSV infection following vaccination. Total follow-up time for each patient will be 1 year from vaccination.

Inclusion Criteria:

• Stable outpatient lung transplant recipients more than 3 months post-transplantation and stable outpatient allogeneic HCT recipients more than 6 months post-transplantation
• Adult equal or over 18 years of age
• Able to comply with blood work at 4-6 weeks post-vaccination
• Able to provide informed consent

Exclusion Criteria:

• Currently pregnant or planning to conceive or breastfeeding
• IVIg or plasmapharesis in last 30 days or expecting in next 30 days
• Previous rituximab in last 6 months
• Active CMV infection with VL > 1000 IU/ml
• Diagnosis of RSV in the past 90 days
• Unwell with acute infection (respiratory or other)
• Any vaccination in last 2 weeks
• History of severe allergic reaction (anaphylaxis) to any vaccination
• Active rejection in last 30 days for lung transplant recipient
• Active GvHD or poor graft function for alloSCT recipient