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Polio Eradication 2011: A Work in Progress
Abstract & Commentary
By Mary-Louise Scully, MD
Dr. Scully is Director, Travel and Tropical Medicine Center, Sansum Clinic, Santa Barbara, CA
Dr. Scully reports no financial relationships to this field of study.
Synopsis: Efforts are ongoing in the attempts to achieve wild polio eradication worldwide, but challenges include adequate funding and political support, vaccine delivery logistics, the issue of vaccine-associated paralytic polio, and vaccine acceptance in resource-poor areas.
Source: Centers for Disease Control and Prevention. Progress Toward Interruption of Wild Poliovirus Transmission Worldwide, January 2010 March 2011. MMWR Morb Mortal Wkly Rep 2011;60:582-586.
As of 2006, the ongoing transmission of indigenous wild poliovirus (WPV) was limited to only four countries Afghanistan, Pakistan, India, and Nigeria. Subsequently, 39 countries that were previously certified as polio-free experienced new outbreaks and polio became re-established in Angola, Chad, Democratic Republic of the Congo (DRC), and Sudan. This MMWR report summarizes the progress toward polio eradication during 2010 and the first quarter (Jan-Mar) of 2011.
Globally 1,291 WPV cases were reported in 2010. This represented a 19% decline from 2009. WPV type 3 (WPV3) accounted for only 87 cases, whereas WPV type 1 (WPV1) accounted for 1,204 cases, a 145% increase from WPV1 numbers in 2009. The cases occurring within the four endemic countries (Afghanistan, Pakistan, India, and Nigeria) accounted for only 232 of the total cases, with 100 cases originating in Pakistan. Of the re-established transmission countries (Angola, Chad, and DRC), there were 159 cases with 100 cases from DRC. The big upswing came from countries affected by WPV1 outbreaks, the largest of those in Tajikistan (458 cases) and Republic of Congo (382 cases).
In the first quarter of 2011, there were 20 cases in Chad, 26 cases in Pakistan, and 36 cases in DRC, which represent a significant increase in cases compared to the first quarter of 2010. Now, as of July 6, 2011, Chad is taking the lead with 85 cases, DRC with 60 cases, and Pakistan with 58 cases of the total 252 cases year-to-date in 2011.1
The good news is that outbreaks in nine countries in 2010 have been halted (i.e., > 6 months since the last reported cases) and six other countries with outbreaks in late 2010 and early 2011 are on track to being stopped. The trouble spots to control will be Pakistan, Angola, DRC, and Chad if the Global Eradication Initiative (GPEI) is to achieve its strategic goals for 2012.
An Independent Monitoring Board (IMB) recently was formed to oversee progress toward wild polio eradication. Their recent report stresses that governments will need to react quickly with added resources and political will if the goal of WPV eradication is to keep on its timeline.
A decade ago, the number of polio cases worldwide had dropped from an estimated 350,000 in 1988 to fewer than 500 in 2001 due to the heroic efforts of the Global Eradication Initiative (GPEI). But during 2002, in India, and later during 2003 in Nigeria, resistance to vaccination led to increases in new polio cases, which then led to spread of these strains to other countries, many of which had been certified as polio-free.
In a recent article in Nature, Heidi J. Larson and Isaac Ghinai from the London School of Hygiene and Tropical Medicine examine the lessons learned from polio eradication efforts over the last 10 years.2 From years of field research, they highlight the importance of community acceptance of vaccines and engagement strategies with local populations to eradicate polio. They cite the story of Nigeria in 2003 as the example of the importance of community support. At that time, five predominantly Muslim states in northern Nigeria boycotted polio vaccination when rumors spread that it was an American conspiracy to spread HIV and infertility. Around the same time, families in the Kano State in northern Nigeria were also suing Pfizer for allegedly unethical practices during the Trovan trial in 1996, so feelings of mistrust were strong. The boycott of oral polio vaccine (OPV) in Kano State lasted 11 months and polio cases in Nigeria went from a low of 56 in 2001 to 1,143 in 2006. From Nigeria poliovirus spread to 15 other sub-Saharan countries and as far as Indonesia, where 303 cases were all traced back to Nigeria.3
The experience in Nigeria, and similar vaccine refusals in India, made the GPEI redirect their strategies away from typical mass communication measures posters, street banners, and radio messages to work with local community members and local institutions to better deliver vaccine information and answer questions or concerns of families. The strategy has worked well. In Uttar Pradesh, India, after implementation of this approach, there has not been a case of polio for more than a year. The London School of Hygiene and Tropical Medicine has also established an early-warning system to detect and investigate public concerns or vaccine rumors before they snowball into larger problems (see www.lshtm.ac.uk/eph/ide/research/vaccinetrust/).
In other areas, the increase in polio cases likely relates more to logistical barriers of vaccine delivery and distribution, coupled with lack of political will to invest both money and resources to polio eradication. This seems to be the case in southern Chad. Here, vaccine acceptance is not an issue, but rather adequate supplies of badly needed vaccine hinder eradication efforts. In areas of Africa embroiled in conflict issues and political upheaval, health and vaccine programs are always in jeopardy.
Last, but certainly not least, is the issue of vaccine-associated paralytic polio (VAPP). OPV has the advantage of low cost, ease of administration, and induction of mucosal immunity. However, the attenuated variants in OPV can mutate and acquire neurovirulence; they can cause paralytic disease in vaccinees and contacts of vaccinated infants and children. Therefore, after mass OPV campaigns, the environment is abundant with a mix of excreted viruses, some of which have the virulence of wild polioviruses. Neal Nathanson in a recent New England Journal of Medicine commentary likens this to "fighting fire with fire."4 Similarly, an epidemiologist involved in the early polio vaccine trials used the phrase "in like a lamb, out like a lion."5
In the United States and many industrialized countries, use of OPV was transitioned to inactivated polio vaccine (IPV) during and after 1998-2000. But the difference in cost between OPV and IPV is substantial. Although most experts see the way forward to eventually include cessation of the use of OPV, how and when that exactly will take place is unclear. Polio eradication will likely involve ongoing coordinated efforts and novel strategies, some of which might include use of IPV in certain geographic areas, bivalent and monovalent OPVs, new development of antiviral agents, and even possibly using fractionated intradermal doses of IPV,6 which would make the product more affordable. Such a multi-faceted approach, coupled with vaccine programs supported and endorsed by local governments and communities, will hopefully end the long and successful reign of polioviruses.