World Polio Day, on October 24 2018, marks a day for celebration of past achievements toward eradication of this vaccine-preventable disease, but also calls into discussion the measures that must be taken to maintain global vaccination and help protect those who are at risk from this disease. With Pakistan, Afghanistan and Nigeria comprising the small group of countries that have yet to stop the transmission of wild poliovirus, we can see how close we are to the second eradication of a human disease in history.

Poliomyelitis, or polio, is an infectious disease caused by poliovirus that is typically spread through contaminated food and water. Five out of 100 cases lead to muscle weakness and paralysis within a few hours or days, and two to five percent of children with these symptoms will die. In many cases, there are no symptoms and the virus can be spread to others for up to six weeks. Because of vaccine innovation and expansion, the global burden has decreased dramatically from 350,000 cases in 1988 to only 22 wild type polio cases in 2017.

When we look at these gains, the power of vaccination is evident. Smallpox is proof that eradication is possible with global collaboration and vaccination programs to ensure that every last child is immunized. Until poliovirus eradication is achieved worldwide, all countries must keep vaccination levels high and continue careful surveillance of polio cases. According to the World Health Organization, if we don’t maintain the defense of vaccination, polio could come back resulting in as many as 200,000 new cases every year within 10 years, all around the world. Yet, vaccination remains unacceptably low in some countries, and they continue to suffer from wild polio outbreaks as a result. In 2017, the estimated global polio vaccination rate was 85 percent, but Pakistan, Afghanistan and Nigeria remained significantly under-vaccinated with only 75, 60 and 40 percent vaccination, respectively.

Vaccination does not only protect against wild type poliovirus. It also prevents outbreaks of vaccine-derived poliovirus, a mutated form of the weakened live virus used in the oral polio vaccine. On rare occasions in severely under-immunized populations, this form of the virus can spread and survive in the population long enough to change into a form that can cause paralysis (watch this video for additional information). Circulating vaccine-derived poliovirus cases now outnumber wild poliovirus, with 68 cases reported globally since January 2018.

An outbreak of vaccine-derived poliovirus has recently developed in Papua New Guinea, spreading to the capital in mid-September and causing fear among residents of the return of this deadly and debilitating disease. As of October 18, there have been 18 cases of vaccine-derived polio in the region and one child has died. Prior to this outbreak, the region experienced its last polio case in 1996 and had remained polio-free since. With childhood immunization rates at only 47 percent in Papua New Guinea, however, this provides the perfect environment for rare vaccine-derived poliovirus mutations to occur. Populations that have full coverage are protected against both vaccine-derived and wild type polio, making it absolutely critical for every country to maintain high levels of vaccination coverage until the last case of polio has been seen globally.

Currently, two vaccinations exist to protect against polio: the inactivated polio vaccine (IPV), created by Dr. Jonas Salk, and the oral polio vaccine (OPV), developed by our namesake, Dr. Albert B. Sabin. During the time when poliovirus was present in great numbers across the globe, a vaccine was needed that was effective, inexpensive, easy to administer and could withstand changes in temperature during delivery to rural environments. Unlike the inactivated polio vaccine, Dr. Sabin’s oral polio vaccine met all of these requirements. Not only did Dr. Sabin develop the vaccine that saved many lives around the world, but he spent much of his time working with governments to ensure that the vaccine was accessible to all children worldwide. While use of Dr. Sabin’s OPV led our efforts toward eradication of wild-type polio, it is being removed from standard vaccination schedules and replaced with IPV in the hopes of eliminating remaining cases of circulating vaccine-derived poliovirus.

In continuation of Dr. Sabin’s efforts toward the global eradication of polio, Amy Finan, Sabin’s Chief Executive Officer, is attending a World Polio Day event in Mexico City where she will be speaking on the discovery and evolution of polio vaccines, and polio eradication around the world. The event, hosted by Sanofi Pasteur, gathers journalists to discuss the present state of polio worldwide, emphasize the significant role that journalists play in informing and educating the public and stress the importance of continued vaccination until worldwide eradication has been achieved.