Polio, or poliomyelitis, has been nearly eradicated by the polio vaccines developed in the 1950’s, sparing countless children and adults from symptoms such as muscle weakness and acute flaccid paralysis. However, there are still three countries (Nigeria, Pakistan, and Afghanistan) that have never been polio-free. These countries are starting to serve as “exporters” of the polio virus, affecting China and Syria, countries that had previously been polio-free.

In 2011, a polio outbreak shocked the northwestern province of Xinjiang, China. There, 21 cases of acute flaccid paralysis were confirmed as wild-type poliomyelitis. China had been certified as polio-free since 2000 and was shocked at the outbreak in Xinjiang. A rigorous investigation and mass vaccination ensued to snuff out the source. A genetic analysis found that the virus had been imported from Pakistan, despite the fact that the originating subject (a 16-month-old girl) and family had no history of travel outside their province in China. China’s response was immediate and vigorous, administering 43 million doses of vaccine in late 2011, and there have been no new cases in China after October 9, 2011. While China was able to attack this outbreak quickly and successfully, Syria's recently confirmed cases of polio have been harder to contain as Syria's public health services are disrupted by civil war.

As humans are the only host for the polio virus, it is theoretically possible to eradicate it. The only way to truly eradicate polio is to vaccinate 100% of people routinely in each country. Poliomyelitis is carried in the intestines and can make its way into the sewage and water systems, but if everyone is vaccinated, it has nowhere to go—outbreaks cannot happen if everyone is immune. The recent outbreaks in China and Syria have been linked to suboptimal immunization rates, therefore leading to susceptible people in these populations.

Nigeria, Pakistan, and Afghanistan remain the three countries that have never been polio-free. Collectively, Nigeria, Pakistan, and Afghanistan have reported 119 cases of polio so far this year, showing a decrease from these nations that reported 182 cases in 2012. Preventing potential outbreaks in these countries will require vaccinating or re-vaccinating millions of people—which is challenging in countries facing civil turmoil. William Schaffner, MD, Professor of Preventative Medicine at Vanderbilt Medical Center urges continued awareness of the importance of vaccination. These outbreaks in China and Syria confirm that global transmission of poliomyelitis can only be prevented if 100% of citizens are vaccinated in a routine and systemized way.

Source: MedPage Today