Heterosubtypic Immune Responses to Influenza in Older People

Vaccination is the principal means of combating epidemic and pandemic influenza. As vaccines induce relatively strain-specific and short-lived antibody responses, annual immunisation with regularly updated vaccine is recommended for seasonal influenza, but would not be expected to protect against a pandemic event. In clinical trials among young adults, at least two doses of avian influenza H5 or H9 subunit vaccine are needed to induce moderate antibody responses. However, studies including older subjects have unexpectedly found that some people aged over 65 yrs have pre-vaccination neutralising antibody to influenza H5 and H9 respectively. These subjects mount a robust antibody response to single dose H5 or H9 pandemic vaccine, suggesting that they are effectively primed to at least some strains of avian influenza. This exploratory proposal focuses on those elderly subjects whose immune systems already exhibit antibodies to H5 with a goal of investigating the humoral and cellular basis of the immune response to seasonal and pandemic vaccination. We will examine neutralising antibody responses to a range of human and non-human influenza viruses before and after seasonal and pandemic vaccination and evaluate cellular B and T cell immune responses before and after pandemic H5 vaccination