History and Management of Polio Eradication
In 1980, smallpox was finally declared to be eradicated globally—a great victory for the world and for epidemiology. Seeing this could be done, we then decided to take on polio. Polio had been, after all, under control in the U.S. at this time with only sporadic vaccine-induced or imported cases. Rather, no wild-type disease had been seen for several years. And, like smallpox, humans were the polio virus’s only known reservoir, making a stop to transmission theoretically plausible. Furthermore, there were two viable and effective vaccines—one need only mobilize the world together in an effort to reach all developing world children still being infected, as they were not all being sufficiently immunized, to maintain an appropriate herd immunity or to stop transmission altogether as in the United States.
What is polio?
Poliomyelitis, though not so identified until 1789 by Englishman Michael Underwood, has probably been around since at least 1580 BC according to historic records indicating a similar paralytic disease (www.endof polio.org). However, the first recorded outbreaks of this so-named virus in Europe were in the early 19th century. Outbreaks were then reported in the U.S. a few years later. Over the next century, epidemics appeared each summer and fall in both the U.S. and Europe, each year becoming more severe. Then in 1952, shortly before the development of the first vaccine, there were a record number of incident cases (over 21,000). Early treatments included the “iron lung” for those with paralysis of respiratory muscles—
Poliomyelitis is classified as an RNA enterovirus, residing in the gastrointestinal tract. It has three serotypes (1, 2, and 3) and is transmitted most often via the fecal-oral route, though oral-oral transmission is also theoretically plausible. One is most infectious from 7-10 days before and after symptoms appear but the virus can still be detected in stool samples for 3 to 6 weeks afterwards (www.cdc.gov). The virus is also highly contagious, with seroconversion rates of 90 to almost 100% among household members of infected individuals (www.cdc.gov).
Polio typically has an incubation period of 6 to 20 days but can range from 3 to 35 days. Its only known reservoir is humans, and is usually passed along by someone who is infected but asymptomatic. Surprisingly, these asymptomatic and undetected cases account for approximately 95% of all polio infections. Furthermore, it is estimated that only one in 200 of all infected develop a paralytic form of the disease.
Also, another 4-8% might contract a minor, nonspecific illness (www.cdc.gov), indistinguishable from an upper respiratory tract infection, fever, and/or nausea and vomiting. An even smaller subgroup are afflicted by a non-paralytic aseptic meningitis which typically lasts about a week and then the individual makes a full recovery.
For those suffering from paralysis (less than 1% infected), one would experience initial paralysis 1 to 10 days after the non-specific viral symptoms aforementioned. Some patients actually recover use of affected limbs but many do not. Usually if paralysis continues for a year or more, full recovery will not be made as in the former case.
There are three types of paralytic polio—spinal, bulbar, and bulbospinal. The former is the most common of the three, usually resulting in a form of leg paralysis. Bulbar polio, the least common, contributes to loss in muscle function adjacent to cranial nerves. The bulbarspinal form represents approximately 19% of cases and is a combination of the former two types. Case-fatality rates for paralytic polio are estimated to be 2-5% for children and 15-30%, but tend to increase among bulbar paralysis cases (www.cdc.gov).
Search for a vaccine
Currently there are two effective vaccines available—IPV (inactivated polio vaccine), developed by Dr. Jonas Salk in 1954, and OPV (oral polio vaccine, based on a weakened live virus), developed in 1957 by Dr. Albert Sabin.
The IPV vaccine was used exclusively in this country until the early 1960’s when OPV replaced it as the preferred form of polio immunization. Now, however, it has been replaced by exclusive use of IPV.
Our own Frederick Robbins, MD, of Case Western Reserve University helped pave the way for the development of these monumental vaccines and shared the Nobel Prize in 1954 in physiology or medicine for his significant contributions to our knowledge of polio epidemiology. It was he, along with his colleagues (John F. Enders, PhD, and Thomas H. Weller, MD), who were first able to cultivate the polio virus in tissue culture. Polio previously was known to be a virus but had never before been thus isolated; rather, work had only been done using monkey specimens. Furthermore, it was only through the achievement of this milestone that it became possible to develop the subsequent vaccines.
After his work isolating the polio virus, Dr. Robbins became very involved with the initial vaccine efficacy trials for the Salk vaccine (IPV). Needless to say, the vaccine was determined to demonstrate sufficient efficacy and soon after became available to distribute to the public.
IPV is highly effective for producing immunity to polio with 90% immunity after two doses and 99% after 3. However, the duration of the immunity is not certain. OPV is also highly effective in producing immunity with 50% immunity after the first dose and 99% after the third. In addition it is considered to provide lifelong immunity. Furthermore, it was through its exclusive use until the 1980’s that the U.S. was able to become polio-free (willd-type virus infection rather).
But now that the U.S. and other countries have been declared polio free, the goal is now to eliminate any vaccine-related infection. Thus, the IPV vaccine has a decided advantage in that it does not contain the live virus as does OPV and cannot cause vaccine-associated paralytic polio (VAPP). In 1996, a combined IPV/OPV regimen was recommended. Then in July of 1999, the exclusive use of IPV was recommended.
According to the CDC, VAPP occurs in one out of every two to three million OPV doses administered. Since 1980, this then accounted for 95% of all cases in the U.S. (approximately 8-10 cases per year with the remaining infections imported from polio-endemic regions). But since the use of exclusive IPV, VAPP has been eliminated, with the last case reported in 1999.
However, in developing countries, OPV still remains the vaccine of choice--it is much easier to administer among populations as it does not require an injection as well as being cheaper to manufacture. Because of this, the benefits far outweigh the risks of VAPP. That is, it would be much greater threat to the community if all the children were not vaccinated as the virus is still endemic.
A commitment toward eradication
As mentioned, the U.S. has been officially declared polio free, witnessing its last wild-type infection in 1979. This particular infection was found to have been imported from the Netherlands. Then in 1994 after mass immunization campaigns, the entire region of the Americas was declared polio free. In 2000 the Western Pacific followed suit. Finally, in June of 2002, the 51 countries of the “Euro” region were declared free of polio as well (www.unicef.org). Overall, as of 2000, new world-wide cases dropped to 2,979, then decreasing to 500 in 2001.
However, this progress could not have been made without all of the extraordinary effort and collaboration that has been a part of the eradication campaign. So how have we come so far, one might wonder?
In 1988 the global eradication initiative was officially launched by the world’s health ministers at the 41st World Health Assembly with a goal of eliminating polio by the end of the century. Furthermore, this resolution specified that this was to be achieved through the Expanded Programme on Immunization (EPI), and through the strengthening of primary health care facilities and structure. Many partners became committed to this goal, such as The World Health Organization (WHO), Rotary International, The Center for Disease Control and Prevention (CDC), as well as the United Nations Children’s Fund (UNICEF).
WHO and UNICEF together lead in the coordination of the operation. WHO works closely with individual country ministries of health, as well as the training and deployment of health workers internationally. In addition, they have been instrumental in establishing certification standard acute flaccid paralysis (AFP—important in coordinating active surveillance activities), as well as the coordination of resources and advocacy. Furthermore, WHO will help determine when and if eradication finally has been achieved using their developed criteria. In fact, Dr. Robbins currently sits on the committee that oversees this process.
UNICEF, like WHO, works closely with endemic country ministries of health, helping distribute vaccines while maintaining the essential cold chain (procedure for maintaining the viability of the live vaccine, transporting it from refrigerated site to site in a standard cooler). In the mid 1990’s the Vaccine Vial Monitor was added to individual vials to determine for sure if the vaccine was still viable.
Rotary International, the largest humanitarian organization worldwide, has provided a substantial amount of funding in addition to a network of volunteers worldwide to assist in the campaign via immunizations themselves as well as training and advocacy programs. They were also instrumental in bringing the polio eradication campaign to the foreground as an international priority, paving the way for the official goal of worldwide polio elimination by the year 2000 (which was changed to 2005 in the late 1990’s, though much progress has been made).
The CDC has been instrumental in providing state of the art lab support, identifying particular outbreak strains of the virus and then finding their origin by matching them to sample strains obtained worldwide. In addition, it has been a leader in providing American funding for immunization campaigns and surveillance activities. Furthermore, many other organizations have been actively involved in the campaign such as the International Red Cross and Red Crescent, Adventis Pasteur, Save the Children, CARE, Medecins sans frontiers, plus many additional groups. And as mentioned, governments of polio endemic countries have also played a key role, committing substantial resources.
Maintaining the “cold chain” in the former Zaire, by Sabastiao Salgado, Brazilian photographer
An action plan
After its success in the Americas, WHO identified several important strategies for worldwide polio eradication. The first was to achieve or maintain high vaccine coverage which theoretically would be 90% (but not always possible due to various reasons to be discussed later). The second was the necessity of National Vaccination Days (NID’s). This was a mass campaign countrywide within endemic areas where all children less than 5, regardless of previous immunization status, would be ideally vaccinated twice, with the two respective doses one month apart. They must be implemented effectively over a period of three years to eliminate transmission.
NID’s in Afghanistan by Sabastiao Salgado, Brazilian photographer
The third point was the continued surveillance for acute flaccid paralysis (AFP). Here individual country health officials investigate any child under the age of 15 with a paralyzed limb, testing his stool sample for polio infection.
Finally, the last was what was designated the “mop-up” campaign with house to house immunizations among the last areas the virus is seen to put a complete stop to transmission. This would be in addition to the NID’s.
Where do we stand today?
Current areas of endemic polio are India, Pakistan, Afghanistan, and parts of the African region. In 2000, there were 20 countries still affected, with only 10 in 2001. Below one can see the spread of new wild type cases in 2002 and 2001, respectively--
As mentioned, much progress has been made as polio eradication has received more and more attention and priority. NID’s increased significantly throughout African countries after 1996 when Nelson Mandela launched his own “Kick polio out of Africa” campaign. This, in effect, helped rally all of Africa with 28 of its countries participating in NID’s by the end of 1996. This had happened previously in China with President Jiang Zemin’s initiative, as well as in Latin America. Truly, politics has played a key role in the eradication progress; it can only be achieved with the necessary political and financial support according to a perspective on the eradication campaign (Hull, 1).
Furthermore, these individuals suggest that the most significant factor in achieving success is the political commitment and accompanying infrastructure within the endemic countries (Hull, 2). Similarly, Dr. Robbins cites lack of funds and infrastructure, in addition to conflict as being significant barriers, as opposed to lack of appropriate technologies or treatments.
Indeed, many of the hurdles have stemmed from unstable regimes and war; at such times of conflict, it is understandably difficult to conduct such a vast immunization campaign. And lapses in immunization can bring about a return of the virus in a population that has not seen polio recently. In 2000 for instance, Cape Verde had not had a case for a decade but when a traveler from Angola immigrated there carrying the virus, 44 people were paralyzed and another 17 dead due to the vast underimmunization (www.endofpolio.org). And to a lesser extent, Burkina Faso had not seen a case since 1997 but then had another confirmed infection December of 2002. Truly, as long as one case of polio remains, all remain potentially at risk.
Polio eradication remarkably has been able to bring many people together and to momentarily put aside hostilities in order to hold mass vaccination campaigns. This first happened in El Salvador in 1985, met with successful results. Warring Sierra Leone also had a similar cease-fire to implement mass vaccination in 1999. Many other nations have followed suit--Afghanistan, the Democratic Republic of Congo, Cambodia, India, and Iraq to name a few.
In each of these instances, the results were only possible with support from WHO, its collaborating agencies, as well as local NGO’s. They worked closely with the warring factions to bring about the necessary cease-fires required for the NID’s and mop up campaigns in areas of open conflict, as well as helping establish some sort of infrastructure for immunizations in areas suffering from the aftermath of conflict (e.g., helping organize refugees and internally displaced persons as well as aiding the remaining health care workers). Once more, politics is at the forefront of the campaign.
Looking to the future
Today, India, Pakistan, and Nigeria maintain the highest rates of wild virus. In 2002, there was a total of nine countries with confirmed wild-type cases. Furthermore, while other countries saw a decrease in cases, India and Nigeria actually saw an increase with that in India being more pronounced; in fact, the vast majority of known wild type cases were traced to these two nations.
The Global Technical Consultative Group for Poliomyelitis Eradication (TCG) reported some concern in these findings. They hypothesized that in the other countries with incident cases appeared to have sufficient supplementary immunization activities (SIA’s—“mop up” activities) to stop polio transmission by 2003 but that India and Nigeria, in addition to Egypt, needed to augment their current efforts and indicated that closing these immunization gaps would require urgent and substantial work to put an end to transmission. They need to follow the lead of Pakistan, one of the remaining “high transmission” countries, which has had consistent quality SIA’s each progressive year (Polio News, December 2002).
India did a good job with its immunization campaigns in 1999-2000 but has recently faltered in its consistency of SIA’s (having only 2 for the entire year) resulting in five times as many cases in 2002 compared to 2001. However, India has just launched the largest ever immunization campaign last February and officials are hopeful.
Nigeria, too, only had 2 SIA’s. This and its lack of local health infrastructure commitment and organization, according to TCG, contributed to their increase in wild-type incidence (Polio News, December 2002).
India and Nigeria need to focus on their health infrastructure, planning regular NID’s, as well as accurately reporting cases of AFP in accordance with the established WHO guidelines for eradication. To be successful, the governments must keep eradication as a priority and work closely with their medical and community leaders, as well as closely collaborating with the aforementioned partner agencies.
As a health official in a rural province in India, one would want to keep an active surveillance for any possible cases (i.e., keeping a careful watch with the help of community leaders for AFP). If a case is spotted, it must be immediately reported to the WHO and partner agencies, as well as the Indian ministry of health to enlist the help of epidemiologists and additional health workers. They would then, in turn, look for any other cases of AFP while at the same time immediately testing the AFP case’s stool for polio virus. One would also want to schedule additional “mop up” vaccinations among those in close contact with him or her, as well as those in surrounding communities. Only with such active and persistent surveillance, in addition to regularly scheduled NID’s can these remaining nations eliminate polio.
And in fact, this is what has been planned for India and other remaining countries at risk. Furthermore, India reported most recently in the Polio News (March, 2003) that they are strengthening their outreach efforts as well (e.g., activities for educating and mobilizing individual communities regarding the importance of immunization efforts and surveillance).
One thing polio has taught us recently is never to be too confident and to expect the unexpected. The Americas had not seen a wild type case in almost a decade. However, in 2000, almost unbelievably, an outbreak of paralytic polio appeared in the island of Hispaniola (i.e., throughout the Dominican Republic and Haiti). It was hypothesized to be a mutated form of the Sabin vaccine virus and was thus able to be so readily transmitted (e.g., it had reverted to something resembling the wild type virus). In fact, its isolated strain was found to be a 97% match with the OPV (Vastag, 2798). Furthermore, due to the underimmunized status of the population, the virus was easily able to infect many. Fortunately in this case, though, epidemiologists and health workers were able to immunize and treat those in close proximity to the infected, thereby containing the out break.
However, this is certainly a concern for the future. Can we simply abruptly cease all immunization as planned once eradication is declared, with the threat of a lingering OPV? Or do we continue to immunize the world but via IPV which might not be a practical goal as the vaccine is much more expensive and more complicated to administer?
There are certainly ethical issues as well—would it be right to risk continued use of OPV in the developing world but keeping the IPV for those of us who are able to have access to the IPV? Fortunately, this instance in Hispanola is considered extremely rare, with only two other such outbreaks documented (and with significantly lower incidence).
And, as Paul Fine and Ilona Carneiro concur, it is very difficult to predict what will happen; hence, there is no easy answer. Therefore, one must continue to maintain active surveillance and gather data while at the same time preparing several contingency plans in the event of further OPV-related outbreaks (1019).
Possible bioterrorism agent?
Could polio follow smallpox’s suit, one might wonder, particularly as eradication becomes more and more of a possibility? Actually, polio is not a pathogen of choice for bioterrorism. Unlike anthrax, smallpox, plague, and others, it can only be transmitted via the oral/fecal route and thus cannot be dispersed aerially (i.e., in this regards it is not nearly as contagious a pathogen).
Nearing the end—is 2005 realistic?
So, one asks Dr. Robbins, will this really come to pass? Actually, as he explained to me, the original 2000 date was just a standard to work toward; rather, it was not derived from any sort of epidemiological algorithm (2005, as well). And this adjusted deadline is theoretically possible--but of course, eradication would not be officially declared until three years after the last documented case according to WHO guidelines, moving the official eradication time to 2008--as long as there were no significant disruption of activities. However, disruptions cannot be overlooked considering the precarious state of affairs in the world today, particularly in areas where the virus is still endemic. Yet many unlikely partnerships have been formed and factions unified throughout this campaign, so it is quite possible the campaign will persevere as it has so far.
Now, though, it is extremely important that endemic countries continue with their immunization campaigns to put an end to disease transmission altogether as previously mentioned. In addition, WHO and the other collaborators must continue to work closely with individual health ministries to assure that NID’s and supplemental immunization activities are consistently and appropriately conducted, particularly in regions of conflict. And finally, and perhaps most importantly, we must continue to keep polio in the forefront of international policy, as politics is such an integral determinant of the campaign’s success. After all, there is an effective vaccine available—it’s just the distribution that’s so difficult.
Bruno, Richard. The Polio Paradox: What You Need to Know. New York:
Warner Books, 2002.
Daniel, Thomas M and Robbins, Frederick C. Polio. Rochester: University
of Rochester Press, 1997.
Fine, Paul EM and Carneiro, Ilona AM. Transmissibility and persistence of oral
polio vaccine viruses: Implications for the global eradication initiative. American Journal of Epidemiology 1999; 150 (10): 1001-1021.
Francis, Thomas, Napier, John A., Voight, Robert B, et al. Evaluation of the
1954 Field Trial of Poliomyelitis Vaccine. Ann Arbor: Edward Brothers, Inc, 1957.
Global Polio Eradication Initiative: Summary Report of 2001 Progress on the
2001-2005 Global Strategic Plan for Poliomyelitis Eradication. Geneva: World Health Organization, 2002.
Gould, Tony. A Summer Plague: Polio and its Survivors. New Haven: Yale
University Press, 1995.
Hull, HF, DeQuadros, C., et al. Perspectives from the Global Poliomyelitis
Eradication Initiative. MMWR: December 31, 1999.
Last, John M. and Wallace, Robert B. Public Health and Preventive Medicine.
Norwalk, CT: Appleton & Lange, 1992, 13th edition.
Nathanson, Neal and Fine, Paul. Poliomyelitis eradication—a dangerous
Endgame. Science 2002; 296: 269-270.
Robbins, Frederick C. Interview: April 4, 2003.
Smith, Jane. Patenting the Sun: Polio and the Salk Vaccine. New York: William
Vastag, Brian. At polio’s end game, strategies differ. JAMA 2001; 286 (22):
www.cdc.gov/nip/publications/pink/polio.pdf, background information on polio.
www.endofpolio.org, general polio eradication data from WHO, UNICEF, Rotary
International, and the CDC.
www.whoafro.org/polio/surveillance_maps/wp2001-2002.html , recent wild virus
www.whoafro.org/polio/certificationcriteria.html , eradication criteria status per
www.whoafro.org/polio/afp_indicators/dec02_as_19feb_03.htm , recent AFP surveillance data.
www.whoafro.org/polio/index.html , general WHO data on polio eradication.
More general websites: