In this open label, single centre, pilot randomized controlled clinical trial the investigators aim to compare the immunogenicity and safety of a new influenza vaccination strategy consisting in the topical administration of imiquimod at the injection site before vaccination vs. a standard intramuscular vaccine injection in SOT recipients and HIV-infected individuals. The investigators planned to enroll 70 outpatients patients (50% solid-organ transplant recipients and 50% HIV-infected patients) regularly followed at the Transplantation center and the Infectious disease outpatients' clinics of the Lausanne University Hospital. Study participants will be randomized in a 1:1:1 ratio to receive the standard intramuscular vaccine (control group) or a topical application of an imiquimod containing cream followed by intramuscular (imiquimod-IM) or intradermal (imiquimod-ID) vaccine injection. After vaccination participants will be followed for a period of 180 days. Blood samples will be drawn at baseline and at day 21 and 180 for assessment of immunogenicity. Safety outcomes will be assessed immediately after vaccine administration, and at day 7 (phone call), 21 and 180.

Inclusion Criteria:

• Provision of written, informed consent
• Age > 18 years
• HIV infection or at least 3 months after kidney transplantation
• Stable outpatients
• Able and willing to comply with the study protocol

Exclusion Criteria:

• Documented egg and/or imiquimod allergy

• Previous life-threatening reaction to seasonal influenza vaccine (i.e. Guillain-Barré Syndrome)

• Previous severe reaction to imiquimod cream

• Pregnancy or breast-feeding

• Patients with autoimmune diseases

• For HIV-infected patients:

  • Current active opportunistic infection

• For kidney transplant recipients:

  • Ongoing therapy for rejection (including steroid pulse or prednisone > 2 mg/kg/day over more than 14 days)
  • Ongoing therapy with IVIG and eculizumab or current and past (<6months) therapy with rituximab