Amid stringent security, a three-day anti-polio campaign has stared in selected districts of Punjab, Balochistan, Khyber-Pakhtunkhwa (K-P) and the Federally Administered Tribal Areas (Fata) on Monday, said Radio Pakistan.
Polio teams will go door-to-door and administer oral polio vaccine drops to children under the age of five in eight districts of Punjab, 20 districts of Balochistan, 17 districts of K-P and Fata during the immunisation campaign.
In Punjab, nearly seven million children will be given anti-polio vaccines while in Balochistan more than 1.7 million children and in K-P and Fata, five million children will be given polio vaccine drops.
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Pakistan is one of just three countries in the world, along with Afghanistan and Nigeria that have endemic polio, a once-common childhood virus that can cause paralysis or death.
However, immunisation efforts have, in the past, been hampered by militants. In January 2016, a suicide bomber killed 15 people outside a vaccination centre in Quetta in an attack, claimed by the banned Tehreek-e-Taliban Pakistan (TTP) and another militant group, Jundullah.
Militants in Pakistan have previously alleged the immunisation campaigns are a cover for Western spies.
Local officials said they had recruited Muslim clerics to promote the immunisations for children after past programmes were met with resistance and even violence by extremists.