Shortly after Bill Gates spoke to the International AIDS Conference in Washington this week, the Microsoft founder, now less boyish and with some gray at his temples, sat down with National Journal to discuss the progress of the international struggle against the disease. Gates's eponymous Bill and Melinda Gates Foundation has been at the forefront of efforts to control AIDS, and this self-described "numeric person" sees trend lines justifying both optimism and continued concern. Edited excerpts follow.

NJ In a period of economic slowdown, when government budgets are strained, will the world be able to continue increasing its financial commitment to this problem?

GATES I think that the rate of increase that we saw over the last 12 years will not continue. Whether you take global health broadly or AIDS in particular, the increase from the rich countries, including the U.S., over this 12-year period has been phenomenal. This get-together celebrates the 8 million people who are alive because of that generosity. But it's a fact that it won't keep going up as it has. I guess there's no item in the U.S. budget that should rule out the possibility of being cut in the face of the deficit and what's going on. But there's no part of the government where the cause and effect is more clear. If you cut this budget, fewer people get drugs and, therefore, more people die.

NJ How serious a threat do you see to the budgets in other Western countries?

GATES It's worse outside the U.S., if you can believe that. Because what some people call the bond vigilantes have showed up in Spain and Italy. So those countries have made cuts to all their budget items. The U.K. is sort of the most amazing, in that they had made a commitment to get up to 0.7 percent of gross domestic product of giving to poor countries — and they're actually going to achieve it ahead of schedule.

NJ What about funding on the private side?

GATES These are very hard things to measure. The research and the delivery of these medicines is over 90 percent funded by governments, and there is no prospect that if that cuts back, there is some actor who could replace any meaningful portion of it. The unfortunate fact is that if one government cuts back, it sort of makes the other governments feel like they get permission to cut back as well.

NJ Do you worry that we're at that downward spiral?

GATES I'm very worried. In a way, you think, "Hey, these people should live, so nobody's going to cut that." But there are people who are in love with missiles, and they say, "Oh, my God. Nobody's going to cut my missiles, because my missiles are so great." Somebody loves every part of the federal budget.

NJ If the money is there, what is a reasonable goal? Is it too much to talk about an "AIDS-free generation"?

GATES I think it's a wonderful phrase. I prefer goals that are more in the five- or 10-year time frame, so you can kind of track what you're doing. The only way to have an AIDS-free generation is to invent a vaccine and get it out in big numbers. And although we're making good progress, we're almost certainly more than 10 years away from being able to deploy that vaccine.

Concretely, during that time frame, what else do we need to do besides getting the vaccine done? We need to get more people on treatment. There's a goal to get that number up to 15 million. That's a very aggressive goal. If we have flat funding, and we're smart about execution, we might be able to do that.

NJ The number of new infections is still double the number of people going on treatment?

GATES We're making progress, but in 2011, more people were infected than went on treatment, so you're not even working into that backlog. I'm a numeric person. A certain statement of pessimism would not capture this situation. But the idea that, hey, it's all rosy, doesn't capture it either.

NJ Is that ratio getting better? Is there a point at which you see those lines crossing?

GATES Absolutely. They've got to cross. When will those two lines cross? About 2015, if we did a really amazing job and there was no decrease in funding. We'd be bringing the infection number down quite a bit, and we'd be bringing the treatment number up quite a bit.

NJ Are there big lessons from the AIDS response for other public-health challenges?

GATES AIDS is such a tough disease that it's caused us to learn so much about the immune system. Just the pure research understanding that this is going to have for vaccines and disease in general is amazing. This is forcing us to answer questions about the immune system that we never had a clue about. And these new tools will have big payoffs in a very direct sense.

Some of these delivery challenges [are applicable, too]. Some of the issues [relevant to distributing AIDS drugs] are very similar to malaria bed nets, TB drugs. And there's some great lessons on how you price things, especially for poor countries. The world got off to a slow start on that initially. The current regime is very good. The drug companies are incented to do the drugs. For the poorest countries, they get marginal-priced stuff. There's a lot of this that will be very beneficial to the world.