D. No polio vaccine. It is not necessary.

Poliomyelitis still occurs in many parts of the developing world. Wildtype polio is occurring now in parts of Pakistan and Afghanistan. However, several other countries in Africa and Asia are experiencing outbreaks of polio cases related to oral-vaccine-derived, virulent mutants that circulate in unsanitary or crowded environments. Vaccination protects against disease associated with both wildtype and circulating vaccine-derived polioviruses. However, immunization in early childhood may not provide adequate protection into adulthood.