Developing vaccines against flavivirus diseases: past success, present hopes and future challenges.

Vaccination still remains the most cost-effective way of protecting large populations against infectious disease. Safe and effective vaccines are available against most pathogenic flaviviruses and in recent years substantial progress has been made in developing vaccines against dengue. Dengue vaccines based on conventional and recombinant DNA technologies are being assessed and initial results are encouraging. Many other experimental vaccines have been developed, but despite the intensity of effort, concerns about the safety of new vaccines appear to be hindering their development. With the global threat from dengue increasing, might it now be the time to consider a less risk-averse approach?