Introduction of inactivated poliovirus vaccine into oral poliovirus vaccine-using countries.

Given the progress already made towards the goal of global eradication of poliomyelitis LE (polio), the risk of paralytic poliomyelitis is changing in many geographical areas. Vaccination against polio will need to continue because of the threat of wild poliovirus importation. However, an increasing number of polio-free countries are determining that the risk of paralytic poliomyelitis associated with continued routine immunization using oral poliovirus vaccine (OPV) is greater than the risk of importation or laboratory handling of wild poliovirus. Some of these countries have introduced inactivated poliovirus vaccine (IPV)--a safe and effective alternative for routine immunization--using one of two approaches: replacement of OPV by IPV and introduction of a sequential IPV/OPV schedule. Countries considering such changes should conduct a thorough evaluation of the epidemiological, financial and operational implications before finalizing a change in policy. Tropical developing countries pose a special challenge for policy formulation on IPV. In these countries, given the unresolved issues related to the immunogenicity of IPV when administered in the WHO/Expanded Programme on Immunization (EPI) vaccination schedule, the continued focal circulation of wild poliovirus on two continents, the relatively high cost of IPV and the operational complexities of introducing this vaccine, WHO does not--as of July 2003--recommend the adoption of IPV alone or in a sequential schedule. It is expected that this position will be reviewed late 2004 and, if appropriate, revised according to the additional information that has become available on IPV effectiveness, logistic implications, and on further progress towards polio eradication. WHO is encouraging operational studies and introduction projects to evaluate these issues.