Why is polio drop given orally??

There are different polio vaccines - one live vaccine which is given orally and one inactivated, which is injected. The main reason for using the live orally vaccine is that it provides excellent immunity (better than the inactivated) since it uses the natural infection route (oral-faecal) in the body where it enters through cells in the intestine. Besides that, it is also much less expensive than the inactivated form, which is a big thing when doing mass immunisations in developing countries.