Polio eradication efforts reached a historic goal recently when Africa was certified as free of wild poliovirus. To mark this milestone, two Task Force polio experts share what this success means for polio eradication globally.
Mark McKinlay, PhD, Director of The Task Force’s vaccine sector, oversees the Polio Eradication Center which includes the Polio Eradication Surge Capacity Support team, the Polio Antivirals Initiative, and the Poliovirus Containment project. Erika Meyer, MPH, is project manager for the Polio Eradication Surge Capacity Support team, which boosts vaccine-derived poliovirus detection and vaccination efforts.
In addition to the Polio Eradication Center’s work, The Task Force’s Training Programs in Epidemiology and Public Health Interventions Network (TEPHINET) supports outbreak response and polio surveillance efforts in Afghanistan and Pakistan, the two countries where wild poliovirus remains.
Q: The efforts of many partners globally have led to significant progress, including a 99% decrease in wild poliovirus cases since 1988 as well as Africa’s recent certification. What does this news mean for polio eradication efforts?
McKinlay: This important advance shows us that if we are capable of wiping out wild poliovirus across the whole African continent, then we should be able to wipe out wild poliovirus in Afghanistan and Pakistan as well as vaccine-derived polio in Africa and elsewhere.
Meyer: This is a huge success, but there are still so many outbreaks to tackle when it comes to polio globally. The situation in Afghanistan and Pakistan shows that we still have a long battle to fight because these countries have both wild poliovirus and vaccine-derived polio outbreaks in addition to a myriad of sociopolitical, infrastructure, and public health challenges. These have made eradication efforts more difficult. But seeing Africa receive this certification energizes the community’s efforts.
Q: What’s the difference between wild poliovirus and vaccine-derived poliovirus, and how do these both play into the eradication effort?
McKinlay: First off, let’s start by defining polio and polio eradication, as the disease is not familiar to many Americans, although it used to be common. Polio is a virus that can cause paralysis, which is transmitted through contaminated water or contact with an infected person’s excrement. Thanks to a successful vaccination program, the U.S. has been polio-free since 1979.
Eradication is defined as the time when there are no cases of wild or vaccine-derived paralytic polio cases and no virus circulating in communities globally. Wild poliovirus is the original form of the virus and has three immunologically distinct types that can cause paralysis and death. Polio types 2 and 3 have been eradicated from the world, while type 1 wild poliovirus is what Africa has just eliminated and which only remains in Afghanistan and Pakistan.
The World Health Organization provides a good explanation of vaccine-derived poliovirus: The oral polio vaccine contains a weakened vaccine-virus that activates an immune response in the body. During this time, the vaccine-virus is also excreted. In areas of inadequate sanitation, this excreted vaccine-virus can spread in the immediate community (and this can offer protection to other children through ‘passive’ immunization), before eventually dying out.
In areas where vaccination rates are high enough – around 80-85% of eligible children – this doesn’t cause a problem. But in places where vaccination coverage is low, this can reintroduce poliovirus to the community and, in very rare instances, lead to an outbreak of paralytic polio. These vaccine-derived outbreaks have occurred in countries in Africa, the Middle East, and South East Asia.
Q: With Africa’s success, what are the greatest challenges facing the eradication effort now?
McKinlay: Getting immunization rates up to protective levels continues to be a challenge and is crucial to fighting both wild poliovirus and vaccine-derived poliovirus, and now the coronavirus pandemic is only making that more difficult. Routine immunization efforts are still running as best they can, but outbreak response vaccination campaigns are mostly still on hold in many countries. Only a few are restarting in the next couple of months.
Meyer: COVID-19 has impacted both disease surveillance of polio as well as immunization coverage. In addition to what Dr. McKinlay mentioned about outbreak response vaccination campaigns, we’re not able to quantify the consequences of missing those campaigns. We can’t access affected communities, so the data is not as accurate as it could be. Also, staff time and other resources such as vehicles, community engagement tools, and laboratory testing supplies, which would usually go towards polio, have been redirected to focus on COVID-19.
Polio is hard to identify in a community because few cases actually show symptoms, so surveillance teams also use environmental sampling from sewage to find places where the virus is present. These samples are sent to laboratories to be tested, but the pandemic has delayed many of the samples from even reaching laboratories. Therefore, we could have more outbreaks than we are aware of right now because the results from these samples are not getting back to ministries of health in a timely manner.
Another issue COVID-19 has caused is the delayed roll-out of a new safer oral vaccine, nOPV2, which provides comparable protection against poliovirus with a marked decrease in the risk for paralysis. This new vaccine should be rolled out in select countries at the end of the year, but the planning for distribution is ever-changing and contingent on the state of the pandemic in those countries.
Q: When polio is eradicated, it will be only the second human disease to receive this status. The other is smallpox, for which The Task Force’s co-founder Bill Foege, MD, helped lead the eradication effort. How are the challenges of eradicating polio different or similar to those of eradicating smallpox?
Meyer: First, having a vaccine that also can genetically mutate to cause the disease itself, as is the case with polio, is a huge difference, which adds a layer of complexity to this effort. This did not happen with the smallpox vaccine. Second, you knew when there was smallpox in a community because it manifested physically in each case, but you don’t always know when polio is present until much later or at all. Polio is very similar to COVID-19 in the sense that cases can carry the disease without any indication.
Then you also have the issue of stakeholder fatigue. The multinational polio eradication effort began in 1988. This effort has been long and tough so successes like the news in Africa are valuable in keeping donors and governments optimistic about reaching our goal.
McKinlay: Dr. Foege talks about the critical importance of the “last mile” in the eradication of smallpox and how they overcame the challenges to rid the world of the deadly disease. While the “last mile” of polio eradication continues to present new challenges including COVID-19, eradication is within reach and we will not give up until it is achieved.
Header photo: Field epidemiologists administering the oral polio vaccine to a child in a hard-to-reach riverine community, in Yenagoa Local Government Area, Bayelsa State, Nigeria as part of the activities during the April 2018 round of the National Immunization Plus Days. Photo courtesy of Tamuno-Wari Numbere, Nigeria FELTP