World Polio Day (October 24) was established by Rotary International over a decade ago to commemorate the birth of Jonas Salk, who led the first team to develop a vaccine against poliomyelitis. Use of this inactivated poliovirus vaccine and subsequent widespread use of the oral poliovirus vaccine developed by Albert Sabin led to establishment of the Global Polio Eradication Initiative (GPEI) in 1988. Since then, GPEI has reduced polio worldwide by 99%.
The polio eradication effort has made huge inroads towards eliminating polio from the planet. In 1988 it was estimated that there were a total of 350,000 cases of poliomyelitis (probably an underestimate); as of this writing there have been 174 cases in 2012. India has been polio-free for over one year, a remarkable achievement. Only three countries have never seen a break in wild poliovirus transmission: Afghanistan, Nigeria, and Pakistan. Continued surveillance and extensive immunization efforts will be needed to remove the last pockets of the disease from these countries.
Because only 1% of poliovirus infections lead to paralytic disease, the 174 polio cases in 2012 translates to 17,400 infections. The virus clearly has the ability to circulate undetected, which can be a problem if surveillance drops. Another thorny issue is how to deal with immunization once the disease has been eradicated. The vaccine strains used for immunization revert to virulence during replication in the human intestine, with the consequence that immunized individuals shed virulent poliovirus into the environment. These viruses will pose a threat to non-immune individuals. How long these vaccine-derived neurovirulent strains will persist in the population is unknown. Therefore we cannot simply stop vaccinating against polio once the disease is eradicated. It will likely be necessary to immunize globally with the non-infectious inactivated poliovirus vaccine until vaccine derived polioviruses are no longer detected.