A successful trial may still give a negative answer; the only really unsuccessful trial is one that does not prove anything. It is still possible to get a lot of information from a 'failure' and there is an ethical obligation to plan any trial to make the most of that information.

UNAIDS makes the point that the sponsors of a trial in a developing country should always aim to enhance the capacity of the country and community where a trial takes place, to deliver treatment and care and to engage in future research.

It is equally reasonable to expect that a community where a full-scale vaccine trial takes place will gain from the extra effort that is made to deliver effective HIV counselling and prevention to volunteers, and the empowerment of volunteers and those who represent the community through the trial process. Put simply, ‘it should be a better place than if the trial hadn’t happened.’

It has been argued that Phase III trials should go ahead for HIV vaccines even without strong evidence from Phase II trials that they will work, on account of what can be learned even from a partially effective vaccine. That said, some evidence suggesting that a vaccine will work is very desirable before proceeding to a Phase III trial. Investors would certainly want this, as mass-production of a commercial product should begin before a trial starts, so there would be no question of differences between the vaccine used in the trial and the one subsequently put on the market.