Virologists are working on a vaccine targeting the virulent form.

The world's leading scientists have stopped talking of vaccine targets, instead favouring terms such as 'incremental advances'.

Next, those genes are filtered for desirable attributes that would make good vaccine targets such as outer membrane proteins.

In both cases the vaccines targeted gp120 and were specific for the geographical regions.

A vaccine targeting several antigens may require delivery to different areas and by different means in order to elicit an effective response.