Polio cases in Pakistan rose by 73 percent during the most intense periods of civil conflict there in recent years, according to a new study.
The report, in the journal Proceedings of the National Academy of Sciences, is one of the first to provide concrete evidence of the impacts insecurity has on efforts to eradicate the paralyzing disease.
Over the past three decades, polio has gone from infecting more than 1,000 children per day to just a handful of cases per year. But experts say as long as the disease circulates anywhere, it remains a threat to unvaccinated children everywhere.
WATCH: The fight against polio continues
Pakistan, Afghanistan and Nigeria are the last three countries on Earth that have not stopped the disease from spreading.
All three suffer from violent militant attacks.
The polio eradication campaign has overcome violence before. Vaccinators have brokered cease-fires in El Salvador, Lebanon, Sri Lanka, the Democratic Republic of the Congo and elsewhere, all of which are now polio-free.
“The question is, is the effect (of insecurity in Pakistan) big enough to really be a barrier to polio eradication?” asked lead author Amol Verma at the University of Toronto.
“Our study suggests that yes, it is,” Verma said.
While polio vaccination teams have been singled out for attacks, including a mother and daughter in Quetta earlier this month, Verma and colleagues looked at violence more generally. They studied casualty figures from terrorist attacks, suicide bombings, drone strikes and gun battles tallied from news reports at pakistanbodycount.org and other sites.
They compared these data to monthly, district-by-district statistics on new polio cases, and data from polio campaigns on the numbers of children reached.
Although conflicts sometimes forced the cancellation of a campaign, the violence had an impact even when vaccinators continued their work.
“Even when vaccination campaigns were carried out in times of high insecurity, the vaccination coverage was about 5 percent lower than in times of low insecurity,” Verma said.
Health workers have been "rather heroic in trying to reach people in these very difficult-to-reach regions," he added, explaining that vaccinators would reach everywhere they could, but knew some areas were too dangerous.
Those unreachable areas added up to more than a quarter-million children not getting vaccinated, and a 73 percent increase in newly paralyzed children.
“Even though it’s only a 5 percent reduction in vaccination rates, that is enough to allow the virus to continue to be circulated and transmitted,” he said.
The study authors acknowledge that campaign officials sometimes falsify records, and population data in Pakistan are limited.
“Despite data collection issues and the inherent difficulty of accurately quantifying levels of insecurity and its impact, the authors have statistically shown that a causal relationship between insecurity and polio incidence exists,” said Richard Sullivan, co-director of the Conflict and Health Research Group at King’s College London, who was not involved with this study.