Normally moral hazard is a concern for charitable activity, but in this case it would be a good thing because it isn't really encouraging negative behavior. If countries intentionally go into debt to eradicate critical diseases with the intention of getting the debt forgiven or paid by someone else, that would be just fine.

Probably not. First this is a highly unusual event, not something other debtors could reasonably expect for themselves.

Second, the money was used to fight polio, a terrible disease. Moral hazard would be Nigerians driving Ferraris purchased by Melinda and Bill. This is not that.

If the Gates want to eliminate such diseases, they must be elated to see effective programs spending their money to do it.

> Moral hazard would be Nigerians driving Ferraris purchased by Melinda and Bill.

The Nigerian kleptocrats have effectively externalized their healthcare costs so that they can buy their Ferraris or more likely a fleet of pimped out G-wagens.

I doubt many people will rush out and make iffy loans on the assumption that Bill Gates will pay them off.

I think this is more related to Gates trying to eradicate polio and showing that he's even willing to incentivize countries that can handle the distribution to do so themselves.

Nevertheless, third parties paying off debt encourages the acquisition of more debt.

Also note that this is the debt of the government, not of the population. There is no guarantee that it will have any objective benefit to the population. Being a third-worlder and having worked for the government and knowing how it works fairly well, I'd rather throw the money from an helicopter than give it to the government. It won't do much good but giving money to the government is almost certain to make people worse off.