In 1988, when the global polio eradication effort began, there were an estimated 350,000 paralytic cases, about 1,000 cases per day on average. In contrast, in 2013, there were 416 reported cases, a little more than one case of paralytic disease per day.
However, success in eradication means a reduction of cases to zero. There are three countries — Pakistan, Nigeria and Afghanistan — which are considered endemic (ie, have never terminated transmission of their indigenous viral strains) and serve as reservoirs to infect other countries that have been free of polio. In fact, spread of polio outside these reservoirs complicates achievement of the eradication goal, since it requires emergency outbreak containment measures and can detract from efforts to terminate transmission in the remaining reservoirs. Additionally, 7 other countries have had wild poliovirus circulation during the last 12 months. As of July 15, 2014, polio cases had been reported from nine countries compared to five countries during the same period of 2013, and one country had environmental evidence of wild poliovirus circulation. During 2014 to date, four countries have exported poliovirus to another country: Pakistan, Cameroon, Equatorial Guinea and Syria. To reduce spread of polio, the World Health Assembly in 2012 declared the transmission of poliovirus anywhere a national public health emergency. On May 5, 2014, the WHO Director-General declared the international spread of wild poliovirus (WPV) a public health emergency of international concern (PHEIC) and made a Temporary Recommendation under the International Health Regulations (IHR), including a recommendation for polio-exporting countries to ensure all residents and long-term visitors (of over 4 weeks) receive a dose of oral polio vaccine (OPV) or inactivated poliovirus vaccine (IPV) before international travel, in order to reduce the potential for further exportations. It also encouraged that other polio-affected countries vaccinate residents and long-term visitors before international travel, even if no exportations have occurred this year to date.
The most important thing that US pediatricians can do to protect their patients from acquiring polio abroad in polio-infected countries (ie, countries where wild poliovirus has circulated during the previous 12 months) and to support global polio eradication is to make sure all their patients are immunized according to the harmonized schedule. If a child is aged younger than 18 years and fully immunized, a booster dose is not necessary before the travel to these polio-infected countries. For children not yet fully immunized, recommendations for accelerating the schedule can be found here. Parents of children who will reside in a polio-infected country for more than 4 weeks should bring with them records of polio immunization on an International Certificate of Vaccination or Prophylaxis (often referred to as the WHO "yellow card") for those children since they will have to demonstrate documented proof of vaccination at the time the child leaves the polio-infected country.
To ensure that US travelers are properly prepared for any vaccination requirements they might face departing polio exporting or polio-infected countries, CDC provides the following additional guidance for children and adolescents who are up to date with IPV vaccination, including those who have completed the routine IPV series. If the child or adolescent will be in a polio-exporting or polio-infected country for more than 4 weeks and their last dose of polio vaccine was administered more than 12 months before the date they will be departing that country, an additional dose of IPV should be given. Children who receive this additional dose as a fourth dose at age 18 months to 4 years will still require an IPV booster dose when aged at least 4 years. If, before departure from the US, the time residing in the polio-exporting or polio-infected country is anticipated to be more than 12 months, available polio vaccine (IPV or OPV) may be administered while in the affected country and 4 weeks to 12 months before departing that country.
The rationale for the recommendations for residents of polio-infected countries who travel is that mucosal immunity can wane over time since vaccination and that while the vaccine recipient may be fully protected against paralysis from polio, they may still be able to transmit virus to others. Thus, the added dose is intended to boost immunity and prevent transmission from polio-infected countries to polio-free areas.