WHO Declares End of Polio Outbreaks in Five African Countries

What does “vaccine-derived poliovirus” mean?

• In under-immunised populations, the weakened virus used in oral polio vaccine can circulate for a long period and rarely mutate into a form capable of causing disease; this is called circulating vaccine-derived poliovirus.
• WHO declared the outbreaks closed after assessments found transmission had been interrupted and population immunity had improved.
• The result shows why high vaccination coverage and strong surveillance remain essential even after wild poliovirus transmission falls.