ALSO READ: USA: New York declares the state of emergency over polio University of Colorado Anschutz Medical Campus's professor of Immunology and Microbiology Rosemary Rochford explains a single case of polio reflects a larger potential spread of the virus because most people infected either don’t show any symptoms or have a very mild illness with symptoms similar to the flu.
Adding on, Rochford explained even without symptoms, an infected person is still excreting virus in their feces, which means they can be a source of infection to others.
The polio declined in the US and globally due to the direct result of the introduction of vaccines and the willingness of the public to accept them.
With the World Health Organisation, in partnership with Rotary International, the Centres for Disease Control and Prevention and other national governments, launched the Global Polio Eradication Initiative in 1998, there were still an estimated 350,000 children with polio in 125 countries.