Twenty-seven years have passed since Heckler’s comment and no vaccine exists. There is a simple reason for this: HIV out-evolves us. HIV can produce around 100 billion new virus particles every day, and it does so with unusual imprecision. When most genetic material is copied with great fidelity, HIV goes for a sloppier approach. It duplicates itself with errors galore, creating a swarm of genetically variable viruses. It leaves a host looking very different to when it entered.

In the face of this rapid shape-shifting, any drug or vaccine soon becomes obsolete. Fighting HIV is like fighting a hydra – there are several heads and every time you lop one off, two more grow in its place.

To tackle this continually