As a virologist who has worked on poliovirus since 1979, I would be remiss if I did not note that today, 24 October, is World Polio Day.Â World Polio Day was established by Rotary International over a decade ago to commemorate the birth of Jonas Salk, who led the first team to develop a vaccine against poliomyelitis.
The polio eradication effort has made impressive progress towards eliminating polio from the planet. In 1988 it was estimated that there were a total of 350,000 cases of poliomyelitis (probably an underestimate); as of this writing there have been 301 cases in 2013, which is unfortunately already more than in all of 2012 (223). Some setbacks to the program include an outbreak in the Horn of Africa, the finding of wild poliovirus (but no paralytic cases) in Israel, and two suspected cases in Syria. Transmission of wild poliovirus has never been interrupted in three countries: Afghanistan, Nigeria, and Pakistan. The good news is thatÂ India remains polio-free, a remarkable achievement.
Currently the eradication effort mainly utilizes the Sabin oral poliovirus vaccine strains (OPV). These vaccines are taken orally and replicate in the intestine, followed by entry into the bloodstream. They induce antiviral immunity in both the intestine and the blood. However, a drawback to using the Sabin vaccines is that the viruses revert to neurovirulence during replication in the intestine. As a consequence, virulent polioviruses are shed in the feces. These can cause poliomyelitis, either in the vaccine recipient or in unimmunized contacts. As wild polioviruses are eliminated, vaccine-derived polioviruses will continue to circulate, necessitating ‘vaccinating against the vaccine’. As a consequence, WHO has proposed a switch to the inactivated poliovirus vaccine, IPV, which if prepared properly cannot cause poliomyelitis.
A very good question is whether the use of IPV can lead to elimination of poliovirus from the planet. Consider the following scenario: at some point in the future the use of Sabin vaccines is discontinued, and all polio immunizations are done with IPV. Vaccine-derived polioviruses will still be present, and possibly also wild polioviruses. As shown by the recent detection of poliovirus in Israel, poliovirus can replicate in the intestines of individuals who have been immunized with IPV. Therefore, in a post-OPV world, immunization with IPV will still allow circulation of vaccine-derived polioviruses. As long as immunization continues at a high rate, there should be no cases of paralytic disease – but we already know that high immunization coverage is difficult to maintain. How long will we need to immunize with IPV before circulation of vaccine-derived polioviruses will stop?
Below are links to resources on polio, provided by David Gold at Global Health Strategies:
- An expert panel including Dr. Bruce Aylward, WHO’s Assistant Director-General for Polio, will discuss the status of eradication today at Rotary International’s ‘Making History‘ event. HelpÂ shareÂ and watchÂ liveÂ at 6:30 PM ET.
- Look out forÂ A Shot to Save the World, a documentary about Jonas Salk’s vaccine discovery, airing on theÂ Smithsonian ChannelÂ today at 8:00 pm ET/PT.
- President-elect of the Asia Pacific Pediatric Association Naveen Thacker wrote anÂ opinion pieceÂ on India’s incredible achievements against polio, and the benefits and lessons India’s experience offers. HelpÂ shareÂ his piece.
- Check out aÂ videoÂ by footballer Leo Messi (tweet), aÂ blog postÂ by Paralympian polio-survivor Dennis Ogbe (tweet),Â aÂ Vaccines TodayÂ blog post by Ramesh FerrisÂ (tweet) and anÂ Impatient OptimistsÂ post on other ways to get involved today.
- Pakistan:Â Thanks to the work ofÂ heroic vaccinators,Â Pakistan has eliminated polio from much of the country. This year, 74% of cases, and 93% during the high season, have occurred in one region: the Federally Administered Tribal Areas (FATA) of northern Pakistan. North Waziristan, in FATA, has been inaccessible since June 2012, and has reported 14Â wild polio cases this year in an increasingly severe outbreak. The program is intensifying immunizations in neighboring areas to prevent spread, but continued inaccessibility in this regionÂ poses a serious riskÂ to the global effort.
- Nigeria:Â Challenges persist in northern Nigeria, particularly in Borno and Kano, but other traditional reservoir areas appear to be largely polio-free — reminders that success is possible. Of particular importance, the northwest of the country, from which polio has historically spread into West Africa, has not had any cases this year. Read and helpÂ shareÂ a recentÂ ScienceÂ articleÂ (available with free registration) that takes an in-depth look at Nigeria’s eradication efforts.
- Afghanistan: Afghanistan’s traditionally endemic Southern Region remains polio-free, with all cases this year linked to cross-border transmission with Pakistan. Next month will mark one year since the last case was recorded in the Southern Region.
- Horn of Africa:Â GPEI partners responded rapidly to the outbreak, and we’re seeing signs of progress: there have been no confirmed cases in the Banadir region of Somalia, the epicenter of the outbreak, or in Kenya, since August. The number of unimmunized individuals in the region still poses a major risk for further spread. Outbreak response will continue aggressively into 2014.
- Possible Polio Cases Detected in Syria:Â Syria reported a cluster of possible polio cases on 17 October that is currently being investigated. The country has been polio-free since 1999, but is considered at high risk for polio due to declining immunization rates.Â Syria’s Ministry of Health is preparing an urgent response across the country, aiming to conduct the first campaign by the end of October. Supplementary immunization activities are being planned in neighboring countries, including Lebanon, Jordan, Egypt, southern Turkey and western Iraq.Â The GPEI has a history of eliminating polio in areas of insecurity. Drawing from past successful efforts in insecure areas, including El Salvador and Angola, the Strategic Plan outlines approaches to eliminating polio in areas of conflict that are informing Syria’s response.
- IMB Report:Â The International Monitoring Board (IMB), tasked with assessing the GPEI effort each quarter, met earlier this month to review the program’s progress, challenges and risks in endemic countries, the Horn of Africa and Israel. The IMB’s report from this meeting will be availableÂ hereÂ on Friday, 25 October