Although global polio cases have dropped by more than 99 percent since 1988, the virus could potentially infect tens of thousands of children annually if vaccination strategies are relaxed. Ending the spread of this highly infectious disease, which can cause total paralysis and death, relies on the eradication of poliovirus.
To date, naturally occurring—or wild polio—types 2 and 3 have been eradicated. In late summer 2020, the World Health Organization’s (WHO) Africa Region was certified wild polio free. Wild polio type 1 remains endemic only in Afghanistan and Pakistan.
Although there is real hope that this disease is nearing an end, poliovirus has recently been detected in Israel, Malawi, Mozambique, Ukraine, and, the United States, and the United Kingdom for the first time in 40 years, providing evidence that gains are fragile.
Achieving long-term global eradication will require a complex, sustained, and multilayered approach involving diagnostic tools, surveillance, vaccines, and a united, global effort toward a polio-free world.
PATH is advancing tools to detect poliovirus in the environment, developing rapid diagnostics, and developing new, safer transmission-blocking vaccines.
Creating affordable, effective surveillance tools
Although poliovirus has been largely eliminated from the world, there were still outbreaks of vaccine-derived and wild-type poliovirus in more than 20 countries in 2021. Environmental surveillance of wastewater is a critical and highly effective means of identifying areas where the poliovirus may be silently circulating.
PATH and the University of Washington collaborated to develop and test a more sensitive and high-impact environmental surveillance tool, the bag-mediated filtration system. This tool can sample 6 liters of wastewater using a highly sensitive filter, which can be easily shipped to a reference laboratory for processing.
This simple filtration system is currently in use in Pakistan and Yemen, helping communities to identify and combat circulating poliovirus quickly and effectively before it threatens to cause an outbreak.
Developing point-of-care diagnostics for low-resource settings
The oral polio vaccine (OPV) has been a key tool in polio eradication, preventing more than 13 million polio cases globally. It uses a weakened version of the live poliovirus that replicates in the intestines for a short period of time while the body builds immunity.
During that period, the weakened poliovirus is shed through human waste. In areas with inadequate sanitation and low vaccination rates, the vaccine virus can circulate in the community for a short time before dying out, sometimes even providing passive immunity to other children while circulating.
However, if the circulation continues for a long period of time in a community with low vaccination rates, in extremely rare cases, the weakened vaccine virus can revert to the dangerous virus it was meant to protect against.
This risk increases when people with primary immunodeficiency diseases (PIDs), a rare class of hereditary diseases, receive the OPV. People with PIDs are unable to mount an adequate immune response to clear the weakened poliovirus from their gut. This means they shed the virus for prolonged periods and increase the risk of mutation into a vaccine-derived poliovirus that can cause polio in unvaccinated people and others who are susceptible to the virus.
Currently, the only methods available to identify individuals at risk for PIDs are laboratory-based and therefore not adequate for use in the remote areas where OPV is most often administered. As such, a point-of-care test that can be performed in low-resource settings is vitally important to limit the ongoing shedding and prevent vaccine virus transmission, both of which will help reduce the likelihood of the emergence of dangerous, vaccine-derived poliovirus.
PATH is currently advancing the development of three rapid diagnostic tests for PIDs, all of which are intentionally designed for use at the point of care in limited-resource settings.
Advancing safer oral polio vaccines
OPV has been a critical tool and the leading vaccine in the global effort to eradicate polio. Fundamental to its success is its ability to prevent person-to-person transmission. However, the current form of OPV presents an eradication obstacle.
As noted above, gaps in OPV coverage have given rise to outbreaks caused by the shed vaccine virus. These vaccine-derived cases now outnumber wild polio cases—a paradoxical sign of the vaccine’s success in bringing the world to the cusp of eradication.
Since 2015, PATH has coordinated a product development consortium to advance a novel oral polio vaccine against type 2 (nOPV2), the polio serotype most often responsible for vaccine-derived outbreaks. Studies have shown that nOPV2 is less likely than traditional OPV2 to revert to a disease-causing form.
Based on these promising data and on the growing concern over type 2 outbreaks, in November 2020 nOPV2 became the first vaccine granted a WHO Emergency Use Listing. Since early 2021, nOPV2 has been used extensively to combat outbreaks in Africa, the Middle East, and Europe, with WHO’s Global Advisory Committee on Vaccine Safety recently “confirming the good safety profile and genetic stability of the vaccine.”
PATH is continuing to advance nOPV2 work with the aim of supporting the manufacturer’s submission for WHO prequalification next year, which will make the vaccine more easily accessible. We are also developing novel oral vaccines against type 1 and type 3 polioviruses, with a Phase 1 study well underway in the United States. These vaccines are also critical investments to help sustain polio eradication.
Supporting vaccine manufacturers to meet global demand
Vaccination against polio will need to continue long after the last cases are recorded, as both wild and vaccine-derived viruses are resilient and will persist for a long time in the environment. The primary polio vaccine of the post-eradication era will be inactivated polio vaccine (IPV), which confers strong individual protection against disease.
Although IPV is less effective than OPV at interrupting person-to-person transmission, it does not perpetuate the presence of the shed oral vaccine poliovirus in the environment. Once communities reach a point where disease transmission risk is low, IPV is the ideal option for long-term routine immunization.
As much of the world transitions from one-dose to multi-dose IPV schedules, manufacturers must be ready to meet growing global demand for years to come. To support these efforts, PATH helps bring new IPV candidates to market, boosts vaccine manufacturers’ production capacity and consistency, and advises on pharmacovigilance for vaccine safety monitoring.
The COVID-19 pandemic has demonstrated the complex global approach that is necessary for eliminating and managing a virulent virus. Eliminating a virus such as polio will require diagnostics, tools, technologies, and vaccines intentionally designed for limited-resource settings.
