New cases of polio linked to the oral vaccine have been reported in four African countries and more children are now being paralysed by vaccine-derived viruses than those infected by viruses in the wild, according to global health numbers…

Source: https://www.theguardian.com/global-development/2019/nov/28/polio-outbreaks-in-four-african-countries-caused-by-mutation-of-strain-in-vaccine