Influenza viruses cause a respiratory illness with highly variable severity, and is a common cause of hospitalization, morbidity and mortality in at-risk groups. HIV infection is associated with increased severity of influenza and greater risk of complications, comparable to that of other high-risk groups (22-24). Currently in Australia there are 2 available influenza vaccine types, the quadrivalent vaccine (for people <65 years of age) and an enhanced trivalent vaccine (for people >65 years of age). In people >65 years of age, the enhanced trivalent vaccine has been shown to induce higher serotype-specific antibody responses and reduce the likelihood of laboratory-confirmed influenza (25). Higher rates of mild injection site reactions have been reported in the elderly, without an increase in systemic or serious adverse reactions (26).

Antibody responses against influenza virus proteins in the vaccine are lower in HIV- infected individuals compared with controls, and appear to be correlated with lower CD4+ T cell counts and unsuppressed HIV viral loads (27-29).  Administration of higher or more frequent doses of vaccine has not been associated with improved immunogenicity (30).  Despite this, a recent meta-analysis of six studies demonstrated a single-dose trivalent (non enhanced) influenza vaccine prevented laboratory confirmed influenza cases with a pooled efficacy of 85% in adults with HIV infection (31). The influenza vaccine should be offered to all HIV-infected individuals annually regardless of immune status, HIV viral load and ART.