James P. Alexander, Steven Wassilak

Infectious Agent

• The infectious agent is poliovirus (genus Enterovirus) types 1, 2, and 3.
• Polioviruses are small (27–30 nm), nonenveloped viruses with capsids enclosing a single-stranded, positive-sense RNA genome about 7,500 nucleotides long.
• Most of the properties of polioviruses are shared with the other enteroviruses.

Mode of Transmission

Fecal–oral or oral transmission. Acute infection involves the gastrointestinal tract and occasionally the central nervous system.

Occurrence

• In the prevaccine era, infection with poliovirus was common worldwide, with seasonal peaks and epidemics in the summer and fall in temperate areas.
• The incidence of poliomyelitis in the United States declined rapidly after the licensure of inactivated polio vaccine (IPV) in 1955 and live oral polio vaccine (OPV) in the 1960s. The last cases of indigenously acquired polio in the United States occurred in 1979.
• The Global Polio Eradication Initiative (GPEI) subsequently led to elimination of polio in the Americas, where the last wild poliovirus (WPV)-associated polio case was detected in 1991.
• In 1999, a change in vaccination policy in the United States from use of OPV to exclusive use of IPV resulted in the elimination of the 8–10 vaccine-associated paralytic poliomyelitis (VAPP) cases that had occurred annually since the introduction of OPV in the 1960s.
• In the United States, two events that occurred in 2005 highlighted the continuing but low risk for poliovirus infection for unvaccinated persons, whether residing in the United States or traveling.
  • A case of imported VAPP occurred in an unvaccinated U.S. adult who had traveled abroad, likely from contact with an infant recently vaccinated with OPV.
  • An unvaccinated immunocompromised infant and four children in two other families in the same small rural community were found to be asymptomatically infected with a vaccine-derived poliovirus, presumably originating outside the United States in a country that uses OPV.
• The GPEI has built upon the success in the Americas and made great progress in eradicating wild polioviruses. There are only four countries where wild poliovirus circulation has never been interrupted: Afghanistan, India, Nigeria, and Pakistan. WPV type 2 has not been detected since October 1999.
• During 2002–2006, 22 previously polio-free countries were affected by importations of WPV type 1 from the remaining polio-endemic countries, primarily Nigeria. In 2007–2008, polio cases occurred in 12 countries following importations of WPV originating from Nigeria or India.
• In spite of recent WPV outbreaks and continued circulation in the four countries where WPV circulation has never been interrupted, the GPEI has reduced the number of reported polio cases worldwide by more than 99% since the mid-1980s. With intensified efforts, worldwide eradication of polio appears feasible in the future.

Risk for Travelers

• Because of polio eradication efforts, the number of countries where travelers are at risk for polio has decreased dramatically.
• At the time of publication, most of the world’s population resides in areas considered free of WPV circulation, including the Western Hemisphere, the Western Pacific region (which encompasses China), and the European region.
• Vaccination is recommended for all travelers to polio-endemic or epidemic areas, including countries with recent proven WPV circulation and neighboring countries. As of September 2008, these areas include some but not all countries in Africa, South Asia, Southeast Asia, and the Middle East. For current information on the status of polio eradication efforts and vaccine recommendations, consult the Travel Notices on the CDC Travelers’ Health website (www.cdc.gov/travel/) or the GPEI website (www.polioeradication.org/).

Clinical Presentation

Clinical manifestations of poliovirus infection range from asymptomatic (most infections) to symptomatic, including acute flaccid paralysis of a single limb to quadriplegia, respiratory failure, and, rarely, death.

Diagnosis

The diagnosis is made by the identification of poliovirus in clinical specimens (usually stool) obtained from an acutely ill patient. Poliovirus may be detected from stool specimens for up to 4 weeks after onset of illness.

Treatment

Only symptomatic treatment is available, ranging from pain and fever relief to intubation and mechanical ventilation for those with respiratory insufficiency.

Preventive Measures for Travelers

• A person is considered to be fully immunized if he or she has received a primary series of at least three doses of IPV, three doses of OPV, or four doses of any combination of IPV and OPV.
• To eliminate the risk for VAPP, OPV has not been recommended for routine immunization in the United States since January 1, 2000, and is no longer available in this country.
• OPV continues to be used in the majority of countries and for global polio eradication activities.

Vaccine

Infants and Children

• Because OPV is no longer recommended for routine immunization in the United States, all infants and children should receive four doses of IPV at 2, 4, and 6–18 months and 4–6 years of age. The fourth (booster) dose is not needed if the third dose of the primary series is administered on or after the fourth birthday.
• If accelerated protection is needed, the minimum interval between doses is 4 weeks, although the preferred interval between the second and third doses is 2 months.
• The minimum age for IPV administration is 6 weeks. Infants and children who have initiated the poliovirus vaccination series with one or more doses of OPV should receive IPV to complete the series.

Adults

• Adults who are traveling to areas where poliomyelitis cases are still occurring and who are unvaccinated, incompletely vaccinated, or whose vaccination status is unknown should receive two doses of IPV administered at an interval of 4–8 weeks; a third dose should be administered 6–12 months after the second.
• If three doses of IPV cannot be administered within the recommended intervals before protection is needed, the following alternatives are recommended:
  • If >8 weeks is available before protection is needed, three doses of IPV should be administered at least 4 weeks apart.
  • If <8 weeks but >4 weeks is available before protection is needed, two doses of IPV should be administered at least 4 weeks apart.
  • If <4 weeks is available before protection is needed, a single dose of IPV is recommended.
• If fewer than three doses are administered, the remaining IPV doses to complete a three-dose series should be administered when feasible, at the intervals recommended above, if the person remains at increased risk for poliovirus exposure.
• Adults (≥18 years of age) who are traveling to areas where poliomyelitis cases are occurring and who have received a primary series with either IPV or OPV in childhood should receive another dose of IPV before departure.
• For adults, available data do not indicate the need for more than a single lifetime booster dose with IPV.

Allergy to Vaccine

• Minor local reactions (pain and redness) can occur following IPV. No serious adverse reactions to IPV have been documented.
• IPV should not be administered to persons who have experienced a severe allergic (anaphylactic) reaction after a previous dose of IPV or after receiving streptomycin, polymyxin B, or neomycin which IPV contains in trace amounts; hypersensitivity reactions can occur following IPV among persons sensitive to these three antibiotics.

Pregnancy and Breastfeeding

• If a pregnant woman is unvaccinated or incompletely vaccinated and requires immediate protection against polio because of planned travel to a country or area where polio cases are occurring, IPV can be administered as recommended  for adults.
• Breastfeeding is not a contraindication to immunization of an infant or mother against polio.

Precautions and Contraindications

• IPV may be administered to persons with diarrhea.
• Minor upper respiratory illnesses with or without fever, mild to moderate local reactions to a previous dose of IPV, current antimicrobial therapy, and the convalescent phase of acute illness are not contraindications for vaccination.

Immunosuppression

• IPV may be administered safely to immunodeficient travelers and their household contacts. Although a protective immune response cannot be ensured, IPV might confer some protection to the immunodeficient person.
• Persons with certain primary immunodeficiency diseases should avoid contact with excreted OPV virus (e.g., exposure to a child vaccinated with OPV within the previous 6 weeks); however, this situation no longer occurs in the United States unless a child receives OPV overseas.

References

1. Sutter RW, Kew OM, Cochi SL. Poliovirus vaccine—live. In: Plotkin SA, Orenstein WA, Offit PA, editors. Vaccines. 5th ed. Philadelphia: Saunders Elsevier; 2008. p. 631–86.
2. Plotkin SA, Vidor E. Poliovirus Vaccine—Inactivated. In: Plotkin SA, Orenstein WA, Offit PA, editors. Vaccines. 5th ed. Philadelphia: Saunders Elsevier; 2008. p. 605–30.
3. CDC. Poliomyelitis. In: Atkinson W, Hamborsky J, McIntyre L, Wolfe S, editors. Epidemiology and prevention of vaccine-preventable diseases. 9th ed. Washington, DC: Public Health Foundation; 2006. p. 97–110.
4. CDC. Progress toward interruption of wild poliovirus transmission-worldwide, January 2007–April 2008. MMWR Morbid Mortal Wkly Rep. 2008;57(18):489–94.
5. CDC. Resurgence of wild poliovirus type 1 transmission and consequences of importation—21 countries, 2002–2005. MMWR Morbid Mortal Wkly Rep. 2006;55(6):145–50.
6. WHO. Global case count. [cited 2008 Sept 16]. Available from: http://www.polioeradication.org/casecount.asp.
7. CDC. Poliomyelitis prevention in the United States—updated recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recomm Rep. 2000;49 (RR-5):1–22.
8. CDC. Poliomyelitis—United States, 1975–1984. MMWR Morbid Mortal Wkly Rep. 1986;35(11):180–2.
9. CDC. International Notes: Certification of poliomyelitis eradication—the Americas, 1994. MMWR Morbid Mortal Wkly Rep. 1994;43(39):720–2.
10. Alexander LN, Seward JF, Santibanez TA, et al. Vaccine policy changes and epidemiology of polio in the United States. JAMA. 2004;292(14):1696–701.
11. CDC. Imported vaccine-associated paralytic poliomyelitis—United States, 2005. MMWR Morbid Mortal Wkly Rep. 2006;55(4);97–9.
12. CDC. Poliovirus infections in four unvaccinated children—Minnesota, August– October, 2005. MMWR Morbid Mortal Wkly Rep. 2005;54(41);1053–5.
13. CDC. Laboratory surveillance for wild and vaccine-derived polioviruses. MMWR Morbid Mortal Wkly Rep. 2008;57(35):967–70.
14. World Health Organization. Conclusions and recommendations of the Advisory Committee on Poliomyelitis Eradication, Geneva 27–28 November 2007. Wkly Epidemiol Rec. 2008;83(3):25–35.