Influenza vaccines

Influenza is a seasonal viral disease that often leads to a high morbidity and mortality both nationally and globally. The mortality from influenza in South Africa is between 6000 and 11 000 deaths every year¹¹.  Individuals who are HIV-infected have a 4-8 fold risk of influenza and are 1.5 times more likely to die as a result of this than HIV-uninfected individuals ^12,13. There are several types of licensed vaccines against seasonal influenza, although only the subunit vaccine is currently available in South Africa. Vaccination against influenza has been shown to be an effective preventive strategy, and many international immunisation guidelines recommend vaccination against the seasonal influenza in HIV-infected individuals. Evidence suggests that HIV-infected individuals may have reduced immune responses to influenza vaccines, especially when CD4+ cell counts are below 200 cells/mL¹⁴.  Despite this influenza vaccination is effective in preventing influenza infection and reducing severity of influenza associated illnesses among HIV-infected persons ¹⁰. Inactivated influenza vaccines administered to HIV-infected individuals have been found to be safe with a vaccine efficacy of approximately 75% in SA, despite a relatively modest immune response as measured by the haemagglutinin inhibition (HAI) assay ¹⁵. Similarly, despite low immunogenicity per HAI assay,  of influenza vaccine in HIV-infected compared to HIV–uninfected pregnant women in South Africa, the vaccine efficacy was 73% against influenza confirmed illness among HIV-infected women ¹⁶. These studies suggest that the conventional immune read-outs which we use for predicting vaccine efficacy for inactivated influenza vaccine, i.e. HAI titres ≥ 40, might not be useful, and underestimate vaccine efficacy in this population.  

The influenza season in South Africa is variable. It can start as early as April or as late as July and lasts between 12 and 25 weeks ¹⁷.

The panel recommends that the trivalent or quadrivalent inactivated influenza vaccine be administered between March and May each year, to all HIV-infected persons, irrespective of CD4+ cell count, HIV viral load, or pregnancy status.