Wild Poliovirus Returns to Previously Polio-Free Countries

Increased circulation of polio in Nigeria sparked other outbreaks in 2009. Image © The Global Polio Eradication Initiative.A worldwide program to eradicate polio, the Global Polio Eradication Initiative, (GPEI) began in 1988. Since then polio has steadily disappeared from countries around the world, leaving only four with endemic polio by 2006: Afghanistan, India, Nigeria, and Pakistan.

Until polio is eradicated, however, all countries remain at risk for imported polio cases–especially those countries with low vaccination rates. In 2009, increased circulation of wild polioviruses in Nigeria led to imported cases and outbreaks in 12 countries in West Central Africa, three of which (in Mali, Mauritania, and Sierra Leone) continued into this year.

Recently the reintroduction of polio into the European region, which has been polio-free since 2002, has also become a concern. In June 2009, the European Regional Commission for the Certification of Poliomyelitis Eradication specifically identified Tajikistan as an area at high risk for polio transmission if wild poliovirus was introduced to the region, particularly because of low immunization rates. In April of this year, wild poliovirus type 1 was identified in stool specimens from individuals with acute flaccid paralysis cases in Tajikistan. As of November 1, 458 laboratory-confirmed cases of wild poliovirus type 1 had been reported in Tajikistan, with 26 deaths, of whom 15 were less than five years old.

More recently, an ongoing outbreak is occurring in the Republic of the Congo. As of November 4, 58 deaths had been reported, with the first case having occurred in early October. Congo’s last case of indigenous polio was in 2000; this outbreak was caused by imported poliovirus. Laboratory testing has confirmed that two cases were caused by wild poliovirus type 1, and additional testing is ongoing to determine the geographic source.

Efforts are underway to end ongoing outbreaks and prevent the virus from spreading to other countries, both in the European region and in the Congo. In the Central Asian republics and Russia, supplementary immunization activities in particular are being planned to prevent the reintroduction of polio into areas known to have low vaccination coverage, including Bulgaria, Georgia and the Ukraine. In the Congo, nationwide vaccination campaigns are expected.

The World Health Organization (WHO) stresses that maintaining high levels of poliovirus immunity in the population can prevent transmission of the disease even if wild poliovirus is imported. WHO states that “All polio-free countries are advised to maintain high levels of immunity against polioviruses at all times through strong routine vaccination programs, adding supplementary immunization activity when necessary.”

Stanley A. Plotkin, MD, who developed the rubella vaccine in worldwide use today and who has worked on poliovirus vaccine, also stresses the importance of maintining high levels of immunity–even in countries like the United States, which has not seen a case of naturally-occuring polio since 1979.

“As long as poliovirus circulates somewhere in the world it can be introduced anywhere people are not vaccinated,” Dr. Plotkin says. “Therefore high individual and population vaccination coverage is necessary.”

Source and more information

Outbreaks Following Wild Poliovirus Importations — Europe, Africa, and Asia, January 2009–September 2010. November 5, 2010. Morbidity and Mortality Weekly Report, 59(43);1393-1399. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5943a1.htm. Accessed 11/9/2010.

Polio in Congo. November 4, 2010. World Health Organization Global Alert and Response. http://www.who.int/csr/don/2010_11_04a/en/index.html. Accessed 11/9/2010.

Global Polio Eradication Initiative: http://www.polioeradication.org

World Health Organization section on poliomyelitis: http://www.who.int/topics/poliomyelitis/en/