Polio cases that arose as a result of the oral vaccine have given the anti-vaccination movement a huge boost, with high-profile figures using it to push their agenda.
A string of polio cases have emerged in recent months. In particular, cases detected in New York city, Jerusalem, and London have made international headlines.
Analysis of these cases has confirmed that they are caused by a rare, vaccine-derived strain of poliovirus. There were 1,081 cases of vaccine-derived polio recorded worldwide in 2020, triple the number in 2019.
The vaccine-derived strain is linked to the oral polio vaccine. It was introduced to the U.S. by Albert Sabin in the 1960s and was instrumental in eradicating the deadly virus.