Reaching toward global polio eradication
Poliomyelitis (polio) is a highly infectious disease caused by a virus that can invade the nervous system and cause permanent paralysis. While polio may strike at any age, it mainly affects children under age five. Vaccines are the only way to prevent this disease, for which there is no cure.
The world is very close to eradicating polio, having reduced the number of cases by more than 99 percent since 1988—the year the international health community came together to form the Global Polio Eradication Initiative. If achieved, it will mark only the second time in history that an infectious disease in humans was fully eradicated, the first being smallpox in 1979.
Completing the job will require continued investment in vaccines and new environmental diagnostic tools that prevent transmission of polio. To this end, PATH is providing leadership and technical support for the development of high-quality and low-cost polio vaccines needed to help achieve eradication and maintain protection post-eradication.
Vaccines to end polio – and maintain protection
Two types of vaccines against polio currently exist—the oral polio vaccine (OPV) and the inactivated polio vaccine (IPV) that is delivered via injection.
OPV has proved to be a powerful tool in high-risk settings, with its ability to halt wild polio transmission. The vaccine is also inexpensive. However, it has two drawbacks: (1) the attenuated virus in OPV can, on very rare occasions, cause vaccine-associated paralytic polio; or (2) mutate into vaccine-derived poliovirus (VDPV) that can circulate in a community for extended periods of time and lead to outbreaks.
The currently available IPVs sidestep these drawbacks and will be necessary in the effort to end polio. However, they lack the transmission-blocking properties of OPV and thus are not ideal in an outbreak situation. They are also much more expensive than OPV.
Given these hurdles, PATH is working with partners on new vaccines that can help the global community complete eradication in the near term, and ensure long-term protection post-eradication.
Additional OPV options
In low-income countries, where more than two-thirds of the world’s population lives, billions of doses of OPV are needed every year for routine immunization and vaccination campaigns in high-risk settings to develop population immunity, stamp out pockets of endemic, wild-poliovirus transmission, and control outbreaks. PATH provides technical assistance to developing-country vaccine manufacturers working on new OPV candidates to drive down the price of OPV even further.
Although the type 2 strain of wild polio has been eradicated, health systems must be prepared to respond quickly to potential outbreaks. To that end, PATH is also working on a new, safer OPV formulation (nOPV) against type 2 poliovirus that can halt transmission during emergency outbreaks without the risk of introducing vaccine-derived poliovirus.
Eventually, all countries will transition from OPV to IPV to completely eradicate wild and vaccine-derived polioviruses. Given that IPV demand will increase significantly over the coming years—even decades—after polio transmission has ended, there is an urgent need to bring down the price and address the global shortage of IPV. PATH is exploring the use of immune-boosting adjuvants; working with manufacturers to scale-up IPV production capacity; and testing dose-sparing methods, such as intradermal delivery.