For most developed countries, polio is considered a virus of the past, eliminated in the years following the breakthrough vaccine discovered by Jonas Stalk in 1952.
China was thought to have been rid of the paralyzing disease in 2000, when they were officially listed as polio-free.
But a 2011 outbreak of a wild strand of the virus in Xinjiang Zhuang Uyghur Autonomous Region in the country’s far west left some observers questioning just how fully it was eradicated. Prior to that, China hadn’t seen an outbreak since 1994.
After years of examining the incident, researchers from China’s Center for Disease Control have released a report tracing the origins of the outbreak, in which 21 people were infected with wild polio and 23 additional cases were found clinically comparable to polio, to Pakistan.
Surprisingly, adults accounted for more than 50% of the cases, with children under the age of 5 being the second largest but most susceptible group. There was only 1 case of unconfirmed polio for those aged 5-14 years old.
The researchers blame part of the 2011 incident on lack on immunizations in the region.
A study conducted in the capital and northern part of Xinjiang in 2010 found 95% of the population under 15 years old were properly vaccinated. But in the south, which shares a border with Pakistan – one of the few places still battling the virus – cultural and geographical factors bar proper immunization practices, they said.
“In southern Xinjiang, most of habitants are Uyghur ethnicity, some of whom have fears about vaccine safety or adhere to religious beliefs, which reject immunizations,” the study, An outbreak following importation of wild poliovirus in Xinjiang Uyghur Autonomous Region, China, 2011, said.
“Some children who live in poor and remote villages are hard to reach for immunization due to transit inaccessibility.”
Following the incident, five rounds of immunization maintenance were initiated between 2011 and 2012 and are effectively thought to have culled the strand.
Still, the outbreak stands as proof that, until the virus is fully destroyed, nowhere is fully protected.
“Until WPV transmission is globally eradicated, the risk of WPV importation exists even in countries which have been certified as polio-free,” the study said.
“Therefore, high coverage of routine immunization should be maintained in children until WPV transmission is globally eradicated.”
It was published online at Bio Med Central in January.