The world was in fear of a new emerging disease threatening to kill millions.
A new variant of H1N1 had arrived. In the UK, 65,000 deaths were predicted. However, to date, these warnings have not materialized.
If this last pandemic has taught something, is how little is known about the unseen world of the virus. But that has not prevented scientists trying.
Horizon is the leading researchers from around the world who are trying to unravel the secrets of the virus to understand when and why they kill.