Modern medicine may not have a significant effect to the populations that live in developing countries due to many factors -
Economically unstable; people from a lower class may not be able to reach the advantages of modern medicine.
Governmental affluence; a countries government may pick other amenities in-front of their people's health and the healthcare system.
Traditional Medicine; some indigenous people are more like to choose traditional medicine instead of modern as it may be classed as 'evil' or witchcraft.
Religion or Culture; some faiths and cultures forbid some types of modern medicine for example stem cell research so those people are more likely to miss out on the advantages of modern medicine.
Sure there are some fools who prefer witch craft, but they are a small minority.
If modern medicine had no affect on these countries then how in the world was smallpox and Polio eliminated from these countries? By using herbs?
Sure governments are corrupt and the healthcare systems may be under budgeted but it is foolish to say that modern medicine has no affect on so called third world countries.