Polio is once again spreading in Pakistan, where officials say more than 1 million children missed their vaccination doses last month, underscoring the challenges they face in eradicating one of the world’s most intractable diseases.

Polio cases are rising ahead of a new vaccination campaign in Pakistan, where violence targeting health workers and the police protecting them has hampered years of efforts toward making the country polio-free.

Pakistan is launching a nationwide polio vaccination campaign on 28 October to vaccinate more than 45 million children under the age of five against paralytic polio. Prior to the latest surge in infections, Pakistan - and its population of more than 240 million - was on the verge of eradicating the disease.