 This altered the strategy envisioned for the discontinuation of vaccination following polio eradication, necessitating an eventual switch to the more expensive and logistically more problematic inactivated polio vaccine, since continued use of the oral inactivated virus would continue to produce such revertant infection-causing strains.The risk of vaccine-derived polio will persist long after the switch to inactivated vaccine, since a small number of chronic excretors continue to produce active virus for years (or even decades) after their initial exposure to the oral vaccine.In a 2012 interview with Pakistani newspaper "Dawn", Dr. Hussain A. Gezari, WHO's special envoy on global polio eradication and primary healthcare, gave his views on obstacles to eradication.