Influenza: current evidence and informed predictions.

Every winter there are sharp rises in medical visits, hospitalizations and deaths from acute respiratory illness worldwide. Influenza is an important cause of these and is the only common viral respiratory pathogen with licensed vaccines available that are safe and effective in preventing disease. Over 50 countries have national vaccination programs focusing on the elderly population and those at high risk. In the USA, healthy children are also now offered the vaccine; routine immunization of the young, who are similarly vulnerable to hospitalization as the old, is likely to become universal. There remains a need for further improvement in vaccine effectiveness (both in the short- and long-term), vaccine administration and compliance. Recent technological developments raise the prospect of using new vaccine types, such as live attenuated and Vero cell-cultured vaccines, that are easier to administer and may induce broader immunity.