Oral polio drops are most popular for its use in various immunization camps organized by various health organizations around the world, particularly in 3rd world nations. However, where economic constraints are not an issue polio vaccine injections are also used.
The oral vaccine rarely causes vaccine associated paralytic polio, in view of which certain developed nations are not using oral polio vaccine anymore, instead using injectable polio vaccine.
Another reason why some nations less prefer the oral polio vaccine is because of the risk of spreading of wild live polio viruses. Oral polio vaccine contains live polio viruses, whereas injectable ones contain killed dead polio viruses.
In certain developing nations where injectable polio vaccine is given, advise is also given to get the oral vaccine too, as part of various polio irradication initiatives that are taken by various health organizations.