The investigators are conducting a double-blinded, placebo controlled randomized trial at the HIV treatment clinic at Helen Joseph Hospital to determine the effectiveness of influenza vaccination in HIV infected adults in South Africa. The significance of the findings from this study will help quantify the burden of influenza illness in African HIV infected adults, as well as assist in making more informed recommendations for the use of influenza vaccine in HIV infected adults and in guiding national policy for preparing for a future influenza virus-pandemic.