Vaccination strategies for the last stages of global polio eradication.

Launched in 1988, the Global Poliomyelitis Eradication Initiative has enjoyed remarkable success. The WHO anticipates isolation of the last wild polio virus during late 2004/early 2005, paving the way for certification of a world free of polio in 2008. However, the ultimate objective of this campaign, discontinuation of polio vaccination, has been jeopardised by two recent developments: the characterisation of vaccine-derived polio viruses (VDPV), and renewed concerns over the risk of bioterrorism. The threat posed by VDPV has led the WHO to recommend discontinuation of OPV usage as soon as possible after eradication certification. Cessation of vaccination with OPV needs to be carefully designed to avoid creating conditions where VDPV will develop. For the longer term, strategies must be designed to guard against the risk of polio reemergence due to long-term VDPV excretors, accidental release of wild viruses or bioterrorism. The main strategies under consideration are a surveillance and response approach or a continuation of vaccination with IPV. Choosing between these strategies will pose a major dilemma for India and for many other countries.