The hunt is on for A Vaccine for Dengue. Dengue fever affects up to 100 million people every year, mainly children.
It kills about 20,000 – and they die from what is known as dengue shock syndrome.
Sanofi Pasteur and GSK, two of the biggest drug companies in the world, have been working on a dengue fever vaccine for some time.
We go to Thailand and Vietnam to see what progress is being made.
Part of a 29 x 25-minute documentary series produced for the BBC. These films can be bought individually or as a series.