Why does transmission and severity of swine flu vary so much between countries?

Answer 1

One of the main reasons some countries have more of a problem with certain Infectious Diseases than others is the overall health of the population. Those with undernourished and frail populace will have much more severity of cases, more cases, and more deaths. This is especially true in the undeveloped nations ("Third World Countries") where health care is less available and where there is a lack of water and other necessary tools for good hygiene. These same countries also typically have a high incidence of HIV/AIDS which leaves the population at much higher risk as do other underlying medical conditions. In the US the native American people and those in the lower socio-economic groups will similarly have more problems for those same reasons. The more crowded countries also will have higher incidence of contagious diseases simply because of the close proximity of person to person in every day life which facilitates the spread of the contagious disease. In poorer countries, the people do not have an option to stay at home when ill, they must go out to work and to find food to eat, this will cause more people to be among groups of others who can pass the disease from human to human while in public.