Polio Eradication in Pakistan

by

Zulfiqar A. Bhutta, Muhammad Atif Habib, Sajid Bashir Soofi

• LAST MODIFIED: 30 March 2017
• DOI: 10.1093/obo/9780199756797-0158

Introduction

Poliomyelitis (polio) is a viral infection that spreads primarily through the fecal-oral route and usually affects children younger than five years of age. After ingestion, the virus multiplies in the intestines and spreads to the nervous system from there, eventually leading to paralysis. Irreversible paralysis is seen in approximately one in every two hundred children that are infected. This paralysis proves fatal in approximately 10 percent of cases when respiratory muscles are involved. Currently, no cure exists for poliomyelitis; however, there are vaccines available which have been successful at significantly reducing the prevalence of this debilitating infection across the world. With a successful vaccination program since 1988, the number of paralyzed persons due to polioviruses has decreased by over 99.9 percent. However, the disease still presents a real threat, especially in Pakistan; this bibliography focuses on the challenges of eradicating disease in this region in particular.

Epidemiology

The epidemiology of polio relates a story of the success of effective vaccination programs. In 1988, there were around 350,000 cases of polio across 125 countries. The goal to eradicate polioviruses worldwide was adopted in 1988 and since then the number of paralyzed persons due to polioviruses has decreased by over 99.9 percent. In 2014, the World Health Organization (WHO) reported 359 cases of paralytic poliomyelitis due to wild polioviruses worldwide (Cases of Wild Poliovirus by Country and Year). In the end of 2015, the remaining endemic areas with wild poliovirus circulation were limited to security-compromised parts of Pakistan and Afghanistan and in Nigeria. In Nigeria, no new cases of polio were reported in 2015, and in September of that year was removed from the list of poliovirus endemic countries (WHO Removes Nigeria from Polio-Endemic List), however the virus emerged again in mid-2016 (Cases of Wild Poliovirus by Country and Year). Despite the dramatic reduction in cases of poliomyelitis, it is proving difficult for the Global Polio Eradication Initiative (GPEI) to finally complete the eradication by interrupting the last chains of transmission in these endemic areas; and export of wild polioviruses from the endemic areas into polio-free countries have occurred in multiple occasions, sometimes causing large outbreaks of poliomyelitis (Hagan, et al. 2015). Polio cases can also be divided into groups by the infecting organism. A majority of the patients reported were infected with the wild poliovirus while only a few were positive for the vaccine-associated poliovirus. The wild poliovirus is the form of the virus found in nature and had three subtypes, one of which was declared extinct in 1999. In contrast, the vaccine-associated form of the virus develops when the attenuated form of the virus that is used for vaccination mutates during replication. However, this is extremely rare and it is estimated that when receiving the first dose of the oral polio vaccine, one in every 2.7 million children develops paralysis. Generally, vaccine-associated strains of the poliovirus do not transmit between hosts as easily as the wild type. However, in certain conditions in severely under-immunized populations the vaccine-associated form of the virus can begin circulating in the community with low herd immunity. WHO reported thirty-two wild poliovirus cases by late 2016 with sixteen cases from Pakistan, twelve cases from Afghanistan, and four cases from Nigeria. Data divided by country for the incidence of polio in 2016 shows that the majority of cases were found in Pakistan and Afghanistan. The difference in incidence rates between Pakistan and other countries highlights the need for a much more effective prevention program in Pakistan. Although the incidence of polio for the year 2016 decreased in Pakistan, there is still a large amount of room for improvement until the last case stands (see the WHO’s Poliomyelitis Fact Sheet, cited under Global Polio Eradication Initiative).

• Hagan, J. E., S. G. Wassilak, A. S. Craig, et al. 2015. Progress toward polio eradication––worldwide, 2014–2015. MMWR Morbidity and Mortality Weekly Report 64:527–531.

  This resource reports regular updates on poliovirus circulation and new cases globally and country specific data.

• WHO. Cases of Wild Poliovirus by Country and Year. Accessed 27/08/2015.

  This resource provides regular updates on poliovirus circulation and new cases globally and country specific data.

• WHO. WHO Removes Nigeria from Polio-Endemic List. Accessed 11/27/2015.

  This resource provides regular updates on poliovirus circulation and new cases globally and also provides country-specific data.

• WHO. Cases of Wild Poliovirus by Country and Year. Accessed 18/06/2016.

  This resource gives regular updates on poliovirus circulation and new cases globally and country specific data.