Both orally administered, live attenuated polio vaccines (OPV) and inactivated polio vaccines (IPV) for intramuscular (or subcutaneous) injection are widely used internationally. OPV has been the vaccine of choice for controlling poliomyelitis in many countries, and for the global polio eradication initiative, because of the ease of oral administration, its superiority in conferring intestinal immunity in immunologically naive individuals, and its low cost. The only very rare adverse event associated with OPV use is vaccine-associated paralytic poliomyelitis (VAPP), which may occur in vaccine recipients or their contacts. The overall risk of VAPP is estimated at 1 case per 2.4 million doses administered. Outbreaks of polio due to circulating vaccine-derived polioviruses continue to be detected occasionally, mainly in areas of low immunization coverage . As long as transmission of wild poliovirus has not been interrupted globally, WHO recommends that OPV should remain the vaccine of choice for routine infant immunization in most countries. However, WHO also recommends that all countries currently using only OPV add at least 1 dose of IPV to the schedule. In polio-endemic countries and in countries at high risk for importation and subsequent spread, WHO also recommends an OPV dose at birth (also called 'zero dose'), followed by the primary series of 3 OPV doses and at least 1 IPV dose.
The primary series consisting of 3 OPV doses plus 1 IPV dose can be initiated from the age of 6 weeks with a minimum interval of 4 weeks between the OPV doses. If only 1 dose of IPV is used in the schedule, it should be given from 14 weeks of age (when maternal antibodies have diminished and immunogenicity is significantly higher) and can be co-administered with an OPV dose. Countries may have alternative schedules based on local epidemiology, including the documented risk of VAPP prior to 4 months of age.
Routine vaccination with IPV alone should be used only in countries with high immunization coverage (> 90%) and at low risk of wild poliovirus importation and spread. A primary series of three IPV doses should be administered, beginning at 2 months of age. If the primary series begins earlier (e.g. with a 6-, 10- and 14-week schedule), a booster dose should be administered after an interval of at least 6 months (four- dose IPV schedule). Some such countries may use a sequential schedule of IPV followed by OPV.
Before travelling to areas with active poliovirus transmission, travellers from polio-free countries should ensure that they have completed the age-appropriate polio vaccine series, according to their respective national immunization schedule. Adult travellers to polio- infected areas who have previously received three or more doses of OPV or IPV should also be given another one-time booster dose of polio vaccine. Travellers to polio-infected areas who have not received any polio vaccine previously should complete a primary schedule of polio vaccination before departure.
Before travelling abroad, persons of all ages residing in polio-infected countries (i.e. those with active transmission of a wild or vaccine- derived poliovirus) and long term visitors to such countries (i.e. persons who spend more than 4 weeks in the country), should have completed a full course of vaccination against polio in compliance with the national schedule. Travellers from infected areas should receive an additional dose of OPV or IPV within 4 weeks to 12 months of travel, in order to boost intestinal mucosal immunity and reduce the risk of poliovirus shedding, which could lead to re- introduction of poliovirus into a polio-free area. For persons who previously received only IPV, OPV should be the choice for the booster dose, if available and feasible. In case of unavoidable last – minute travel, travellers should still receive one dose of OPV or IPV prior to departure, if they have not received documented dose of polio vaccine within the previous 12 months. Some polio-free countries may require such travellers from polio-infected countries to provide documentation of recent vaccination against polio in order to obtain an entry visa, or they may require that travellers receive an additional dose of polio vaccine on arrival, or both.
All travellers are advised to carry their written vaccination record (patient-retained record) in the event that evidence of polio vaccination is requested for entry into countries being visited. Preferably travellers would use the IHR 2005 International Certificate of Vaccination or Prophylaxis. The certificate is available from the WHO web site at http://www.who.int/ihr/IVC200_06_26.pdf