The Polio Eradication Initiative has made considerable progress as the largest public health program in history. The number of countries endemic for polio has decreased from more than 125 to just three-Afghanistan, Nigeria and Pakistan-since the World Health Assembly declared the goal of global poliomyelitis eradication in 1988. In the same period, 2.5 billion children have been immunized against polio and the number of cases worldwide has declined dramatically from 350,000 to 223 in 2012, with more than 10 million cases of polio prevented.
Of the three serotypes of wild poliovirus, the causative agent of poliomyelitis, type 2 was last detected in 1999 and type 3 in November 2012. Until wild poliovirus type 1 has been eradicated all countries remain at risk of imported cases of polio, as occurred in Australia in 2007 from Pakistan. Most of the polio cases reported in 2013 have been due to a large outbreak in Somalia and Kenya caused by wild poliovirus from Nigeria.
The challenge of polio eradication is greater than that faced by smallpox due to most poliovirus infections being asymptomatic with < 1% presenting with paralysis and a requirement for multiple immunisations. The realization that under certain conditions outbreaks of poliomyelitis due to vaccine derived poliovirus can occur has led to the planned cessation of oral polio vaccine usage after wild poliovirus eradication.
Australia has clinical and virological surveillance schemes to detect imported poliovirus and monitor its polio-free status. The clinical scheme focuses on children < 15 years of age with onset of acute flaccid paralysis, while virological surveillance has two components: (1) Enterovirus surveillance involving public sector diagnostic virology laboratories and (2) Environmental surveillance comprising the testing of sewage from sentinel sites.