Eradicating polio

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Science  06 Nov 2015:
Vol. 350, Issue 6261, pp. 609
DOI: 10.1126/science.aad7294

On 20 September 2015, the Global Commission for the Certification of Poliomyelitis Eradication (GCC) declared that type 2 wild poliovirus had been eradicated. The GCC examined reports from 189 of 195 countries around the world and studied separate data [held by the World Health Organization (WHO)] from the remaining countries. According to WHO, nearly 2 million appropriate clinical samples had been tested, and no type 2 wild polioviruses were found. The announcement is the first step toward eradicating all three wild poliovirus types. But this landmark will only be declared when the GCC is confident that there have been no wild virus cases of any type for 3 years.


“A second human virus may soon be consigned to history.”

The last case of type 3 wild poliovirus occurred in northern Nigeria 3 years ago. In theory, declaration of its eradication could happen now. However, the polio programs from 18 African countries have not yet been scrutinized by the African Regional Certification Commission to ensure that no cases have been missed. This assessment will happen 3 years after each country's last case of any wild poliovirus. By the end of 2017, all African countries must have gone successfully through their regional commission's scrutiny, and no wild virus cases must have occurred. If that happens, all countries in the world will submit their data to the GCC and type 3 wild poliovirus eradication can be declared.

That will leave just the type 1 poliovirus, which is still circulating in Pakistan and Afghanistan. To date, the 51 cases of 2015 are far fewer than the 334 cases reported in 2014. This is probably the result of improved access to vaccination in key regions. But there are always fewer cases the year after high numbers are reported, because natural infection reduces the numbers of children susceptible to polio in the following year. The polio programs in both countries must further accelerate their activities. If transmission is interrupted by the end of 2016, then the world can be declared polio-free in 2019.


One underappreciated consequence of the path toward eradication is that all polioviruses (wild and vaccine strains) in laboratory, research, and manufacturing facilities will have to be destroyed or securely contained. Last month, the WHO Strategic Advisory Group of Experts on immunization reaffirmed April 2016 as the date for the globally synchronized withdrawal of type 2 oral poliovirus vaccine. This first step toward the eventual phased removal of all three vaccine types brings urgency to completing the destruction, and securing the containment, of type 2 wild polioviruses in all facilities. The fewer the places that hold either polioviruses or specimens that could contain polioviruses, the more certain we can be that they will not be released inadvertently. This means that the vaccine industry will have to comply with high levels of assurance of containment in their manufacturing processes. Researchers and institutions holding samples collected from places where there could have been polioviruses must ensure that these are destroyed or secured under appropriate biocontainment levels. Countries will need to submit inventories of all laboratories to the GCC for review, and manufacturers and laboratories planning to retain type 2 polioviruses will need to be inspected for compliance with containment guidelines.

In 1980, smallpox was declared eradicated after a global immunization campaign led by WHO. But 2 years earlier, a year after the last natural smallpox case (in Somalia), there was an inadvertent release of smallpox virus from a research lab in the United Kingdom, from which one person died. While we wait for Pakistan and Afghanistan to stop the spread of type 1, we must prepare to safely and securely contain all polioviruses. A second human virus may soon be consigned to history. Until then, the whole world, especially countries with fragile health systems, remains at risk of this disease.

  • A.A. and D.M.S. are writing on behalf of the GCC: Anthony Adams (Chair), Supamit Chunsuttiwat, Arlene King, Rose Gana F. Leke, Yagob Al Mazrou, and David M. Salisbury.

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