On the brink of eradication: Polio over 30 years
To mark our 30th anniversary, Infectious Disease News will be examining some of the chronic conditions and infectious diseases that have impacted pediatric care over the past 3 decades.
In 1988, the World Health Assembly established the Global Polio Eradication Initiative, which set out to eradicate wild-type polio from the world by 2000. This came nearly 200 years after Michael Underwood, a physician in the U.K., first described the illness.
In that timeframe — the span of almost 2 centuries — numerous developments in medicine and politics made the eradication of polio a viable goal. The first was an outbreak of polio in New York City in 1916 “that spread fear not only in New York City but throughout the country,” according to Stephen L. Cochi, MD, MPH, senior advisor of the Global Immunization Division at the CDC.
“That was really when polio made it on the map as a public health problem in the U.S.,” he said. “The next big event was in 1921, when Franklin D. Roosevelt developed paralytic polio at the age of 39 years. Those are some of the biggest events in the pre-vaccine era.”
The injectable, inactivated vaccine, or IPV, was developed by Jonas Salk in 1955. Less than a decade later, Albert Sabin produced the live-attenuated oral polio vaccine, or OPV. However, the inactivated vaccine had some drawbacks, according to Michel Zaffran, MEng, director of polio eradication at the WHO and chair of the Global Polio Eradication Initiative’s strategy committee.
“It triggers an excellent protective immune response against all three types of poliovirus in most people,” Zaffran said. “However, it needs to be administered by a trained health worker with sterile injection equipment and procedures, which have limitations when trying to reach populations on a large scale and in hard-to-reach locations. It also induces low levels of immunity in the intestine, so when a person immunized with IPV is infected with wild poliovirus, the virus can still multiply inside the intestines and be shed in the feces, risking continued circulation.”
The development of the polio vaccines “very dramatically changed the course of polio in the U.S. as well as in the world,” according to Cochi.
Polio was eliminated from the U.S. in 1979, largely due to widespread vaccination. Since then, one of the three serotypes has been eliminated from the world, and the virus remains endemic in only three countries – Afghanistan, Nigeria and Pakistan.
“Poliovirus type 2 has been eradicated. That is a major development,” Walter A. Orenstein, MD, professor and director of the Influenza Pathogenesis & Immunology Research Center at Emory University School of Medicine and associate director of the Emory Vaccine Center, said in an interview. “We may be on the verge of eradicating type 3; no cases of poliovirus type 3 have been seen in Nigeria since 2012. The current problem really is poliovirus type 1, which is in Afghanistan, Nigeria and Pakistan.”
The next step is eradication of poliovirus type 1 from the three countries in which it is still endemic. Zaffran said that such an accomplishment “will be one of the greatest public health achievements in history,” although he and the other clinicians who spoke with Infectious Disease News all agreed that it will not be an easy task to accomplish.
Vaccination, surveillance remain critical
The primary strategies that will make the eradication of polio possible include routine vaccination and surveillance. However, these activities are difficult to maintain in the three countries where polio is still endemic, especially Afghanistan and Pakistan, due to issues related to security, a lack of trust in health care providers and hard-to-reach populations.
Supplemental immunization activities are one strategy used to combat these issues. These programs, which aim to reach children who miss mass vaccination campaigns, include house-to-house vaccination in affected areas and vaccination campaigns at border crossings and in camps for individuals who are displaced.
“Routine vaccination and surveillance are the standard steps that have been used to stop transmission everywhere, but in those three endemic countries that remain, they are very challenging steps,” Cochi said. “That is why there is still the last foothold of the polio virus in those countries.,”
The circumstances that make routine vaccination a challenge also lead to issues with consistent, effective polio surveillance, another critical step in eradication.
“We have had to take extra steps in these countries to try to strengthen the polio disease surveillance system, including the laboratory network, and conduct environmental sampling, or sewage sampling, in selected areas to look for the virus and get the best picture possible about where it does and does not still exist,” Cochi continued.
More effective use of these strategies in Afghanistan, Nigeria and Pakistan will require support from around the world, according to Zaffran.
“Countries where polio survives are conducting vaccination and surveillance activities in very difficult circumstances. Their health workers operate in complex, insecure areas,” he said. “To enable these activities, all three polio-endemic countries will require the support of the global community.”
Distrusting health care providers may also contribute to the issues surrounding vaccination and surveillance. Working directly with the citizens who live in areas where polio is still endemic is another part of eradication.
“We have to engender community trust,” Cochi said. “We have to get community and religious leaders actively involved in the program, educate those leaders and, where possible, provide other health interventions to lower suspicion among the population that there is something peculiar about offering this oral polio vaccine for free.”
These efforts must continue once the virus has been eradicated entirely, to maintain the progress that has been made.
“We need to continue surveillance for at least 3 years after the last cases are detected and go through a process called global certification, which we have done for type 2 poliovirus and smallpox,” Orenstein said. “We will need to stop use of all oral polio vaccines and, for a period, use the injectable vaccine to provide some level of population immunity, in case there is a reintroduction.”
Containment of polio specimens that remain in labs will also be critical once the virus is eradicated from Afghanistan, Nigeria and Pakistan.
“To truly eradicate polio and maintain a polio-free world, stocks of the virus in labs and vaccine production facilities must be destroyed or contained safely and securely according to strict biocontainment requirements,” Zaffran said.
This is a process that has, to some degree, already started, according to Cochi.
“We have to make sure there is good containment of polio to minimize, or eliminate, the risk of the virus leaving the lab,” he said. “This is a process that is gradually taking place by decreasing the number of labs and facilities that have specimens of poliovirus. For those that continue to have specimens, we have to make sure that they are handled under very high containment, like what we would use for the most dangerous or deadly viruses, including Ebola or smallpox.”
The trajectory of polio in the last 30 years began with a global commitment to end polio. Since then, there has been a decline of more than 99.9% in the number of wild poliovirus cases, but the 1988 resolution from the World Health Assembly has not yet been fully accomplished.
The four incidences of polio — three cases of wild poliovirus type 1 and one case of vaccine-derived poliovirus type 2 — in Borno, Nigeria in the second half of 2016 highlight the ongoing foothold the virus has in the world, according to Orenstein.
“We are not completely there yet,” he said. “We had zero cases in 2015, but there were four cases in Nigeria in 2016, where there are problems with insurrection and security. However, even there, we are still doing much better than we were. In 1988, when eradication was set as a goal, there were an estimated 350,000 cases of polio and the virus was considered endemic in approximately 125 countries. Now, in 2016, we’re down to three countries that are considered endemic.”
Cochi stressed the importance of maintaining vaccination and surveillance efforts after the world is deemed free of polio.
“Only the type 1 wild poliovirus — the naturally occurring virus — continues to circulate. Two out of three types are gone,” he said. “After type 1 is eradicated, we have to continue surveillance for polio, including environmental surveillance. We have to continue vaccination. The Strategic Group of Experts on Immunization, which advises the WHO immunization policy, is tentatively recommending that polio vaccination continue to occur for at least 10 years after the world is certified as polio-free. That means, probably, that polio vaccination will continue through the next decade.” – by Julia Ernst, MS
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Disclosure: Orenstein reports serving as a consultant to the Bill and Melinda Gates Foundation. Cochi and Zaffran report no relevant financial disclosures.