ISLAMABAD (AP) — Pakistan detected one more polio case in the restive northwest bordering Afghanistan, raising the country's tally of the infectious disease to 50 cases this year, officials said Wednesday.

Pakistan and Afghanistan are the only two countries in the world where the spread of polio has never been stopped.

The sudden rise in cases of polio, which is an infection caused by a virus that mostly affects children under 5, has hampered the country's yearslong efforts to make it a polio-free state.

The latest case was detected in Tank, a district in Khyber Pakhtunkhwa province where militants often target polio workers and police assigned for anti-polio campaigns, according to a statement by the National Emergency Operations Centre for Polio Eradication. Pakistan has reported 50 such cases this year, it said.

Most polio cases this year were reported in the restive southwestern Balochistan and Khyber Pakhtunkhwa provinces bordering Afghanistan, where 23 confirmed cases have surfaced, according to data from the World Health Organization. That’s up from six cases in 2023.

Hamid Jafari, the WHO director for the Eastern Mediterranean, said last week the forced repatriation of Afghans from Pakistan was a major setback to polio eradication and has led to a “massive and unpredictable movement” of people within the two countries and across borders.

“The virus moved with these populations,” he told a virtual discussion hosted by the Global Polio Eradication Initiative.

He said there were other reasons for the rise of polio in Pakistan, including the impact of militancy in some parts of the country.

Pakistan regularly launches campaigns against polio despite attacks on the workers and police assigned to the inoculation drives. Militants in Pakistan often target police and health workers during campaigns against polio, claiming the vaccination drives are a Western conspiracy to sterilize children.

More than 200 polio workers and police assigned for their protection have been killed since the 1990s, according to health officials and authorities.

Earlier this month, a bomb attached to a motorcycle exploded near a vehicle carrying police officers assigned to protect polio workers in Balochistan, killing nine people including five children.