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Since 1988 when the Global Polio Eradication Initiative (GPEI) was launched, there has been a a 99% reduction in the incidence of Polio around the globe.
As of 2006, the virus remained endemic in only four countries: India, Nigeria, Pakistan, and Afghanistan.
But since that time, 39 countries previously thought free of the virus have experienced outbreaks following importation of the wild polio virus.
Transmission of the disease has been reestablished in Angola, Chad, Democratic Republic of the Congo (DRC), and Sudan (cite MMWR May 13, 2011 / 60(18);582-586).
In their most recent update (as of 6/28/11), the GPEI states:
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There have been 241 cases globally in 2011 (216 wild poliovirus type 1 - WPV1 - and 25 WPV3), compared with 456 cases at the same time in 2010 (399 WPV1 and 57 WPV3).
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Over 80% of cases this year come from just three countries: Chad, the Democratic Republic of the Congo and Pakistan.
Despite the progress made to date, eliminating that last 1% of the polio cases has proven to be more difficult than originally hoped. Remote areas in developing countries, places often embroiled in local conflicts, remain stubborn pockets of transmission.
Today, the World Health Organization is reporting the first recorded instance of WPV3 (wild polio virus subtype 3) in Asia in 2011. The case involves a 16 month old child in a remote area of Pakistan, and re-stokes concerns that this all-but-eliminated serotype continues to circulate.
First a link to the WHO report, then a little more on WPV.
Poliomyelitis in Pakistan
7 July 2011 - Pakistan has reported wild poliovirus type 3 (WPV3) isolated from a 16-month old child with onset of paralysis on 9 June 2011, from a conflict-affected, inaccessible area of Khyber Agency, Federally Administered Tribal Areas (FATA). This is the only case of WPV3 detected in Asia in 2011. WPV3 transmission in Asia is on the verge of elimination, with the last case occurring more than six months ago, on 18 November 2010 (also from Khyber Agency, FATA).
Confirmation of continuation of WPV3 transmission in tribal areas of Pakistan has significant implications for the global effort to eradicate WPV3, particularly as Asia is on the verge of eliminating circulation of this strain. The detection of WPV3 in Pakistan represents the risk that it may spread from this transmission focus to other WPV3-free areas of Asia and beyond. Globally, WPV3 transmission is at historically low levels in 2011, with other circulation of this strain restricted to parts of west Africa (17 cases in Côte d'Ivoire, Guinea, Mali and Niger), Nigeria (five cases) and Chad (three cases). The risk of onward spread of WPV3 is deemed as high by the World Health Organization (WHO), particularly given large-scale population movements within Pakistan, between Pakistan and Afghanistan, and expected large-scale population movements associated with Umrah and the upcoming Hajj (pilgrimage to Mecca, Kingdom of Saudi Arabia) in the coming few months.
A little background on the polio vaccine, and the return of the virus is in order.
There are three serotypes of Polio (WPV1, WPV2, and WPV3). Serotype 2 was declared eradicated in 1998 only to re-emerge as a vaccine derived poliovirus (VDPV) in Nigeria in 2006.
Since then, rare cases of VDPV have been reported around the world. They arise due to the use of the oral polio vaccine (or OPV), which uses a weakened (attenuated) live virus instead of the polio shot, which uses an inactivated virus.
The OPV is mainly used in developing countries since it is cheaper, and it doesn’t required trained medical personnel to administer. As a side benefit, as a live-virus vaccine it is shed in feces, and can therefore indirectly inoculate other children via the fecal-oral route.
And most of the time, that works just fine.
But rarely, particularly in children with weakened immune systems who may shed the virus for months, the virus can mutate back to its wild-type virulence, and re-enter the community.
As long as all children are fully vaccinated, that isn’t usually a problem. But as countries approach a `polio free’ status, they often reduce their vaccination programs in order to save money.
They may stop vaccinations entirely, or shift to using bivalent (type 1 & 3) oral vaccines, instead of the trivalent formulation.
Either way, that can open the door for VDPV strains to emerge.
The CDC’s Polio information page has this to say about Vaccine Derived Polio Viruses:
Is there a difference in a disease caused by a VDPV and one cause by wild poliovirus or OPV?
No, there is no clinical difference between paralytic polio caused by wild poliovirus, OPV, or VDPV.
I've heard that VDPV has been found recently in the United States. Is this true?
In 2005, a VDPV was found in the stool of an unvaccinated, immunocompromised child in the state of Minnesota. The child most likely caught the virus through contact in the community with someone who received live oral vaccine in another country 2 months prior. Subsequently, seven other unvaccinated children in the the child’s community were shown to have poliovirus infection. None of the infected children had paralysis. For more information specifically related to this case visit http://jid.oxfordjournals.org/content/199/3/391.full.pdf
(exit) In 2009, an immunoncompromised adult developed vaccine-associated paralytic polio (VAPP) and died of polio-associated complications. VDPV was isolated, and the infection likely occurred where her child received OPV 12 years prior.
Where do vaccine-derived polioviruses come from, and should I be concerned if there is a case in the United States?
VDPVs can cause outbreaks in countries where vaccine coverage with OPV is low. Long-term excretion can also occur in people with certain immunodeficiency disorders. Because OPV has not been used in the United States since 2000 and vaccine coverage with IPV is high, it is unlikely that any vaccine-derived poliovirus (VDPV) seen in the United States would become widespread.
Also, polio vaccination protects people against naturally occurring polioviruses and vaccine-derived polioviruses.
There are some scientists who fear that until developing countries move away from using the attenuated OPV - and adopt the inactivated vaccine - that the last vestiges of polio will remain impossible to eradicate.
Today’s report deals with an increasingly rare wild-type serotype, as opposed to a vaccine derived variety.
While the battle against polio has not been completely won, the global elimination of the virus is tantalizingly within reach.
For more on the Global Polio Eradication Initiative (GPEI) you can visit their website and read their strategic plan to eliminate this scourge over the next few years.
