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Polio

Poliomyelitis (polio) is a highly infectious viral disease transmitted by contaminated drinking water and sewage. There are three types of wild polioviruses: serotype 1, 2, and 3. The polioviruses replicate in the gastrointestinal tract and further invade the nervous system, and can cause permanent limb paralysis. While polio can strike at any age, it mainly affects children under age 5. Vaccination against polio is the best way to prevent polio disease. There are two types of vaccines currently used against polio—a live oral polio vaccine (OPV) delivered as oral drops, and inactivated polio vaccine (IPV) delivered via injection. Due to global vaccinations and improved sanitary conditions, the world is very close to eradicating polio. Over 2.5 billion children have been vaccinated since 1988 and the number of polio cases per year is down by 99 percent. Currently the poliovirus serotype 2 has been eradicated globally and types 1 and 3 combined cause fewer than three hundred cases worldwide. While there has been remarkable progress in polio eradication, more affordable vaccines are needed to complete the job of eradicating polio and maintain protection post eradication.

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Polio disease

  • Poliomyelitis (polio) is a highly infectious disease caused by poliovirus that invades the nervous system and can cause permanent paralysis.
  • There are three serotypes of poliovirus (1, 2, and 3). Immunity to one serotype does not protect against the other serotypes.
  • Wild poliovirus type 2 has been eradicated and cases of type 1 and 3 combined are less than three hundred cases worldwide.
  • Polio can strike at any age but it mainly affects children under age 5.
  • The world is very close to eradicating polio. Over 2.5 billion children have been vaccinated since 1988 and the number of polio cases per year is down by 99 percent.

Polio vaccines

  • There are two types of vaccines against polio—a live oral polio vaccine (OPV) delivered as oral drops and inactivated polio vaccine (IPV) delivered via injection.
  • OPV is a trivalent vaccine that contains attenuated (weakened) viruses for serotype 1, 2, and 3. The live vaccine viruses can also shed from immunized individuals and circulate as circulating vaccine-derived poliovirus (cVDPV) in a community.
  • Among the cVDPV, the serotype 2 cVDPV are the most common with over 90% circulating strains of this serotype. The cVDPV will continue unless global community makes the transition from OPV to IPV after wild poliovirus is eradicated.
  • The live attenuated vaccine virus can mutate in some cases, and result in vaccine-associated paralytic polio (VAPP), although this is rare, occurring once for every 2.7 million first doses of the vaccine.
  • In most wealthy countries where poliovirus is eradicated, the only vaccine used is IPV. The current price of IPV (>$3/dose) is out of reach for low- and middle-income countries, and they rely mostly on OPV ($.14 -.17/dose) for mass vaccination campaigns.
  • In order to accomplish complete global polio eradication and to ensure protection against poliovirus post-eradication, new vaccine and surveillance tools are needed:
    • Lower cost OPV for maintaining population immunity, for stamping out pockets of endemic wild poliovirus transmission, and for controlling outbreaks.
    • Much more affordable IPV to contain and end VDPVs and sustain population immunity against poliovirus post eradication.
    • Affordable IPV-containing pediatric combination vaccines for future birth cohorts in low-income countries.

References

Page last updated: October 2014.

Photo: PATH/Gabe Bienczycki.