ISLAMABAD, PAKISTAN - Pakistan this week has marked a full year without detection of wild polio cases, a landmark development in a country where the disease annually paralyzed approximately 20,000 children in the early 1990s.

The South Asian nation of about 220 million people and neighboring Afghanistan are the last two wild polio-endemic countries in the world.

While polio paralyzed 84 children in Pakistan in 2020, the most recent infection of the wild virus, known as WPV1, was recorded on January 27, 2021, the lowest number of reported cases in the country ever.

"Twelve months without detection of WPV1 cases in Pakistan is an encouraging epidemiological signal but must be taken with caution," Dr. Hamid Jafari, director of polio eradication for the World Health Organization Eastern Mediterranean Region, told VOA.

"It does not mean that WPV1 has been eradicated from the country or the circulation of virus has stopped in Pakistan," he said.

"Poliovirus does not follow calendar years - it is a seasonal virus, and right now we are in the low-transmission season when the virus is weakest," Jafari said.

Surveillance efforts continued to detect the virus in environmental samples as recently as last month, pointing to continued transmission of WPV1 in Pakistan.

Pakistani officials and international partners recognized that challenges to reaching all Pakistani children with vaccines also persist in key areas of the country, including parts of the Khyber Pakhtunkhwa province bordering Afghanistan.

"The biggest danger we face right now is complacency. This is the time we need to pull out all stops to intensify our surveillance and actively search for the virus -- be it in tracking down the remaining chains of transmission, or any remaining affected children," Jafari said.

He noted that countries in the final stages of their anti-polio efforts, notably India and Nigeria, have shown that low-level transmission can persist for a significant amount of time before the strain is completely eradicated.

Nigeria officially eradicated wild polio in 2020, leaving Pakistan and Afghanistan as the only countries where the disease is still endemic.

Setbacks, skepticism

Pakistan formally launched national anti-polio drives in 1994 and tens of thousands of vaccinators have since been staging regular inoculation campaigns across the country.

Polio vaccination drives in Pakistan have suffered setbacks in recent years due a variety of factors, including attacks on vaccinators and police personnel guarding them.

A man with a child leaves after polio vaccination of his child at a health center, in Peshawar, Pakistan, Jan. 24, 2022.

The latest attack came on Tuesday when gunmen shot and killed a policeman providing security for polio vaccinators in a northwestern town, Kohat. No health workers were harmed in the incident.

Outlawed militant groups, which claim they are fighting for establishing their brand of Islamic law, or Sharia, in Pakistan, see the polio vaccine as an effort to collect intelligence on their activities. Pakistani officials denounce the claims as ridiculous and dismiss the militants as criminals and thugs.

Fundamentalist religious groups in conservative rural parts of the majority-Muslim nation reject the immunization as a Western-led conspiracy to sterilize children.

The false information has triggered attacks during vaccine campaigns, killing scores of health care workers and security forces in the last decade or so.

Pakistani officials insist the attacks on polio teams have particularly increased since 2011, when the CIA arranged a fake vaccination campaign with the help of a local doctor, enabling U.S. forces to locate and kill fugitive al-Qaida chief Osama bin Laden deep inside Pakistan.

"The progress that has been made to date is largely thanks to sustained commitment by leaders at all levels, including at the highest levels - and now is the time to ensure commitment and effort must now be sustained and intensified," Jafari said.

Only four cases of wild polio were confirmed in Afghanistan in 2021, down from 56 cases a year before. The U.N. said the lowest ever polio transmission in the country has provided an unprecedented opportunity to achieve eradication. The end of the Afghan war has also fueled hopes a polio-free Afghanistan is within reach.

Last year in November and December, U.N. officials say health workers were able to deliver polio vaccinations to 2.6 million Afghan children who had previously been inaccessible due to the conflict.

"Close coordination with Afghanistan is being strengthened to detect poliovirus and improve vaccination among cross border mobile populations," Jafari said.