South-East Asia is facing an explosion in increasingly virulent and geographically mobile dengue fever.
Reported cases have increased from 300,000 a year in the 1980s to 925,000 since 2000 — and poor surveillance makes the WHO estimate that cases actually top 50 million annually. Vaccines are urgently needed.
But increasing human mobility means that all four strains of the virus often circulate simultaneously, and although infection gives immunity to individual strains, it can seriously exacerbate subsequent infections with different strains. So vaccines must target all four strains simultaneously.
Getting immune response levels right for tetravalent vaccines is tricky, partly because it is difficult to grow dengue virus in laboratories, and also because there is no convenient animal model for the disease.
But researchers are closing in on a solution, and three potential vaccines are now in phase II trials.
Scientists are persevering with conventional live attenuated vaccines, but also have chimeric candidates, including one that combines a yellow fever virus with several key dengue genes.
Charity-funded preparations for large clinical trials, including epidemiological data collection and standardisation for diagnostic protocols, mean that promising vaccines should quickly move to phase III clinical trials — knocking years off the process.