The purpose of this study is to assess the safety and effectiveness (immune response) to a licensed H1N12009 influenza vaccine in HIV-infected adults. The study will enroll 150 adults (ages 20-59 years). Participants will be randomized into 2 groups and will receive either one dose or two doses of a licensed H1N1 vaccine. Study procedures include: medical history, blood samples and completing a memory aid. Participants will be involved in study related procedures for approximately 6 days.

During the first wave of the H1N12009 pandemic in Canada, adults with immune deficiency were more likely to die with severe infections than were other Canadians. Of 76 deaths attributed to date to this new virus, 37% occurred in persons with immune system compromise. Adults with human immunodeficiency virus (HIV) infection constitute a significant proportion of the at-risk population with over 56,000 affected individuals. Most such individuals retain some capacity to respond to influenza vaccination. The dosing regimen for the pandemic vaccine will be based on limited studies in the general population, leaving open the question of whether HIV-infected persons can respond satisfactorily to the recommended dosing. Availability of an adjuvanted formulation of the pandemic vaccine may improve responsiveness but two doses may be required for the best possible response. Thus it would be optimal to evaluate the safety and immunogenicity of the pandemic vaccine among the earliest HIV-infected persons to receive it, to inform the subsequent vaccination of others.

The objectives of this study are three-fold:

1. To evaluate the safety and immunogenicity of H1N12009 influenza vaccine in a convenience sample of adults with HIV infection.
2. To compare immune responses of subjects randomized to receive either one or two doses of adjuvanted vaccine to identify the optimal regimen.
3. To complete this evaluation soon after the pandemic vaccine becomes available so as to inform the subsequent use of the vaccine in HIV-infected persons.

Inclusion Criteria:

• Laboratory-confirmed HIV
• Written informed consent
• Adults 20-59 years of age

Exclusion Criteria:

• Allergies to eggs, thimerosal or gentamicin sulphate
• Life-threatening reaction to previous Flu vaccine
• Bleeding disorder
• Pregnancy
• Receipt of blood or blood products in past 3 months
• Chronic illness
• Previous lab-confirmed H1N12009 infection
• Receipt of any non-study H1N12009 or Seasonal Influenza vaccine for 2009/10