The World Health Organization (WHO) has dubbed Pakistan’s northwestern city of Peshawar the world’s “largest reservoir” of polio and declared that almost every 2013 polio case in Pakistan could be genetically linked to the virus strains in the city of four million.

“With more than 90 percent of the current polio cases in the country genetically linked to Peshawar, the [city] is now the largest reservoir of endemic poliovirus in the world,” the WHO said in a statement. The WHO has called for urgent action to keep vaccinations ongoing in order to put a halt to the spread of the disease, which affects mainly children. Vaccination involves a quick tongue drop, but efforts to eradicate the virus in rural areas is difficult often due to a widespread belief that vaccines can cause infertility or other complications.

The WHO reported that every sample taken from Peshawar’s sewage system tested positive for a very contagious wild polio virus strain. “As much of the population of the area moves through Peshawar, the city acts as an amplifier of the poliovirus,” the WHO said in a statement.

As if the situation wasn’t dire enough, vaccination efforts are difficult to carry out properly as Pakistani militants continue to attack health workers, as the Taliban banned vaccinations in 2012. “The prevailing security situation in Peshawar has seriously affected the quality of polio campaigns in the city and is resulting in inadequate coverage of children against the virus,” the WHO said. Security needs to be improved in certain areas of Pakistan in order for vaccination efforts to continue, and for eradication to succeed.

Polio (poliomyelitis) is an infectious disease that mostly affects children under the age of 5. According to the WHO, one in 200 infections leads to permanent paralysis, which can lead to death.

Though polio cases around the globe have decreased by 99 percent since 1988, there are three countries left where polio remains endemic — Pakistan, Afghanistan, and Nigeria. In the past year, Pakistan was the only nation that experienced a rise in polio cases. Meanwhile, due to the conflict in Syria, polio has resurfaced in poor areas throughout the country where it is nearly impossible to carry out vaccination efforts due to political turmoil. The WHO also linked the outbreak in Syria to the strain from Pakistan.

Polio has been eradicated from most countries for years, and India recently celebrated three years without a reported case.

Peshawar provincial health minister Shaukat Ali Yousafzai told the AFP, "We are committed to eliminating the disease and doing our best despite continuous attacks on polio workers."