Every three years, we have to go to the governments and say, okay, you know you're saving millions of lives and even though your budgets are tight, helping Africa avoid this disaster really is a priority.

If you withdraw the incredible focus on polio, it will spread back, and in poor countries you'll get something like 100,000 cases a year. So by being very intense and getting the cases down to zero, what you do is you avoid all the future cases.

Why do people benefit in inverse proportion to their need? Well, market incentives make that happen.

Imagine, just for the sake of discussion, that you had a few hours a week and a few dollars a month to donate to a cause - and you wanted to spend that time and money where it would have the greatest impact in saving and improving lives. Where would you spend it?

I'll get to see many disease eradications. and we're seeing a lot of progress.

With tech companies, whoever's the leader is always questioned, you know. They say, 'Is this the end of them?' And - there's more - more times people think that's the case than it really is the case.

I have this very positive view of the world getting better and better. The list of things that could be huge setbacks is not very long: A nuclear war, climate change and epidemics.