The Polio Endgame

By Bruce Aylward, M.D, and TadaTaka Yamada, M.D., (New England Journal of Medicine)

[Excerpts] Infection with poliovirus can have devastating  consequences, including paralysis and death. In 1988, a year when an  estimated 350,000 or more children were paralyzed by polio, the World  Health Assembly initiated a global effort to eradicate the infection once  and for all. It was an audacious undertaking, given that the virus  circulates largely undetected, requires laborious cell-culture  techniques to confirm infection, and is tackled with vaccines that  provide imperfect protection in the gut.

Initially, the number of  polio cases and countries with infections fell rapidly, particularly as  financing and political support increased in the mid-1990s. The last  case of paralytic poliomyelitis caused by the serotype 2 wild poliovirus  was detected in 1999. The number of new polio cases caused by the two  remaining wild serotypes had decreased by 99% between 1988 and 2005, but  progress had stalled and there was a danger of failure when wild polio  viruses were reintroduced into large areas of Africa and Asia. By the  end of 2009, sustained investments in innovation had produced a new  bivalent oral poliovirus vaccine (OPV)1 and novel tactics for reaching children who had been missed  consistently by vaccination campaigns.

……..Of  the three risks associated with OPV, the most frequently realized one  is vaccine-associated paralytic poliomyelitis (VAPP). This risk will  disappear with the cessation of use of OPV. Outbreaks caused by  circulating VDPVs are rarer than VAPP cases, but new diagnostic tests  have confirmed their regular emergence, particularly that of serotype 2  circulating VDPVs, which were found in eight of the nine countries  reporting VDPV outbreaks between 2008 and 2010. The persistence of such  an outbreak for more than 4 years in Nigeria highlights the importance  of reducing the risk of VDPV outbreaks when OPV use ceases and of  actively managing any persisting outbreaks.

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