Pakistan on Monday launched a door-to-door campaign to vaccinate millions of children against polio, after evidence of cross-border transmission from neighboring Afghanistan.

The National Institute of Health confirmed the detection of poliovirus genetically linked to the virus found in Nangarhar province of Afghanistan in November 2022 in Lahore, Pakistan’s second-largest city, in January.

The Health Ministry said in a statement said “this is the first evidence of cross-border transmission in more than a year,” the Health Ministry said in a statement.’’

The five-day campaign will target more than 6 million children under the age of five in 39 districts of the country.

Partial campaigns will be conducted in 30 districts that include the areas bordering Afghanistan, Afghan refugee camps and high-risk mobile populations in the southern city of Multan.

Health Minister Abdul Qadir Patel said the presence of wild poliovirus with genetic links to the virus in Afghanistan is evidence that the virus is moving with people and circulating in communities.

“Poliovirus on any side of the border is a threat to children in both countries. Only repeated doses of the oral polio vaccine can offer life-long protection,” he said.

In January, two environmental samples collected from two separate sites in Lahore tested positive for wild poliovirus.

Pakistan and neighboring Afghanistan are among the few countries in the world where new polio cases still surface.

Pakistan had only one case of polio in 2021 but 20 cases were reported last year, all from the violence-stricken province of Khyber Pakhtunkhwa bordering Afghanistan.