NOWSHERA, Pakistan (CNN) -- Ikra lies on her mother's lap, her eyes stained with tears. She wants to go and play with the other children but she can't even move, her mother says.

She's just 17 months old, but already Ikra has been paralyzed by polio in one of the three countries in the world where the disease remains endemic.

Last year, 198 cases of polio were reported in Pakistan, a 15-year high, and the largest number of cases recorded anywhere in the world, according to the Global Polio Eradication Initiative (GPEI), a joint program to eradicate polio led by the World Health Organization (WHO), United Nations Children's Fund (UNICEF) and Rotary International.

Children under the age of five are most vulnerable to the disease, which is spread by a virus and leads to paralysis and, in some cases, death.

Since a global vaccination campaign was launched in 1988, the number of cases worldwide has dropped dramatically, although along with Pakistan, polio is still endemic in Afghanistan and Nigeria, according to the GPEI.

Pakistan is causing particular consternation among health officials who say their efforts to vaccinate more children are being frustrated by the CIA's use of a fake vaccination program last year to gather intelligence on Osama bin Laden.

In a letter to CIA director General David Petraeus in February, InterAction, which represents nearly 200 U.S.- based non-government organizations, expressed "deep concern" about the fake campaign.

"Among other factors, international public health officials point to the distrust of vaccines and immunization campaigns as contributing to the lack of progress in eradicating the disease in Pakistan," it said.

"This distrust is only increasing in light of reports about the CIA campaign," it added.

Bin Laden was killed in a raid by U.S. Navy SEALs in May 2011 at a heavily fortified compound in Abbottabad, in northeastern Pakistan.

Local news reports linked Pakistani doctor Shakeel Afridi to the U.S. intelligence operation, alleging he tried to gain access to bin Laden's compound through the fake vaccination scheme.

Pakistan recently sentenced Afridi to 33 years in jail for providing financial and medical assistance to the now defunct militant group Lashkar-e-Islam.

Officials originally told CNN Afridi was charged with treason for spying for the United States.

"The incident with Dr. Shakeel Afridi definitely impacted not only our polio vaccinations but other vaccination programs as well," said Arshad Ahmad Khan, a doctor at Nowshera health department in the country's northwest.

Alem Zeb said he rejected free polio vaccination drops for his children, aged 7 and two because they were "poison."

"The polio drops destroy the sperm," he told CNN from his home in Peshawar, in the country's northwest. "It's a campaign by the West to disable Muslim children," he said.

"The U.S. provides funds to destroy Muslims and to make them slaves through such campaigns," he added.

Aid groups have recruited religious leaders to assure anxious parents that the vaccinations are not part of Western plan to sterilize their children.

"We go from door to door in every neighborhood to people who refuse [to vaccinate their children] and for whatever reasons they give, and assure them," said Mohammad Asim Head of the religious school called Idara-e-Taleem-ul-Quran in comments distributed by UNICEF.

"For some, a visit by the Imam is good enough," he added.

At the start of this year, the Global Polio Eradication Initiative (GPEI) launched an Emergency Action Plan with the aim of vaccinating enough children to halt transmission of the disease by the end of this year.

So far their blitz has succeeded in reducing the number of cases so far this year, with only 16 recorded in Pakistan at end of May, compared to 36 during the same period last year, according to a joint statement from aid groups.

However, to stop polio transmission completely, aid groups said at least 95% of all children in Pakistan must be immunized during multiple campaigns throughout the country each year.

Oral drops need to be administered several times to each child before they become fully immunized.