In solid organ transplant (SOT) the receipt of influenza vaccine in an influenza season is associated with decreased disease severity as demonstrated by the presence of pneumonia and ICU admissions. Different strategies have been assessed to optimize vaccine efficacy and immunogenicity of the influenza vaccine in the solid organ transplant recipient (SOTR). The primary objective of the study is to evaluate the immunogenicity of 2 doses of the high dose influenza vaccine utilizing neutralizing antibody assays. A control group receiving 1 HD influenza vaccine will be included.

Inclusion Criteria:

• >=18 years old who underwent a solid organ transplant (Liver, lung, heart, kidney, pancreas) > 1 year prior to enrollment
• At least 1-year post-transplant
• Able and willing to provide informed consent
• Able and willing to undergo all study activities throughout the duration of the study

Exclusion Criteria:

• Confirmed pregnancy
• Receipt of ATG or carfilzomib within the past 3 months
• Receipt of rituximab within the past 3 months
• Receipt of basiliximab within the past 3 months
• Prednisone dose >= 20 mg/day at the time of enrollment
• History of a severe allergy to influenza vaccine (i.e. Guillain Barre syndrome, anaphylaxis or angioedema)