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.