[Influenza vaccination. Effectiveness of current vaccines and future challenges]

Seasonal influenza is an annual challenge for health-care systems, due to factors such as co-circulation of 2 influenza A subtypes jointly with 2 influenza B lineages; the antigenic drift of these virus, which eludes natural immunity, as well as immunity conferred by vaccination; together with influenza impact in terms of morbidity and mortality. Influenza vaccines have been available for more than 70 years and they have progressed in formulation, production and delivery route. Recommendations on vaccination are focused on those with a higher probability of severe disease, and have a progressively wider coverage, and classically based on inactivated vaccines, but with an increasing importance of attenuated live vaccines. More inactivated vaccines are becoming available, from adyuvanted and virosomal vaccines to intradermal delivery, cell-culture or quadrivalent. Overall vaccine effectiveness is about 65%, but varies depending on characteristics of vaccines, virus, population and the outcomes to be prevented, and ranges from less than 10% to almost 90%. Future challenges are formulations that confer more extensive and lasting protection, as well as increased vaccination coverage, especially in groups such as pregnant women and health-care professionals, as well as being extended to paediatrics.