More about polio

This page provides a link to PATH's work on polio and information about the disease and related vaccines.

On the PATH website

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 2013.