QUETTA, Pakistan (Reuters) - Pakistan began a special five-day polio immunisation campaign in the southwestern city of Quetta on Monday for children under five after a rare strain of the virus was found in sewage samples, officials said.

A boy receives polio vaccine drops by anti-polio vaccination workers along a street in Quetta, Pakistan January 2, 2017. REUTERS/ Naseer Ahmed

Local officials said they had recruited Muslim clerics to promote the immunisations for 400,000 children after past programmes were met with resistance and even violence by extremists.

“The religious leaders were ... asking the people to give their children anti-polio drops in their sermons in the mosques in rural areas of Baluchistan,” said Syed Faisal Ahmed, coordinator of the local Emergency Operation Centre.

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.

Last year, Pakistan reported a record low of 19 cases, Ahmed said, with only one of them in Baluchistan province, of which Quetta is the capital.

The new campaign follows the detection of the rare Type 2 strain of polio in sewage samples taken by the World Health Organization in November, Ahmed said. The WHO reported the findings last week.

No cases of the Type 2 strain have been reported in humans in Quetta but it has been added to the vaccine as a precaution. The more common type of polio is Type 1, with no human cases of Type 2 reported for more than a decade.

“We have achieved major goals in combating polio disease, but still we have to strive more to declare Pakistan a polio-free country,” Ahmed said.

Immunisation efforts have in the past been hampered by Islamist militants. Last January, a suicide bomber killed 15 people outside a vaccination centre in Quetta in an attack claimed by the Pakistani Taliban and another militant group, Jundullah.

Militants in Pakistan have previously alleged the immunisation campaigns are a cover for Western spies.

The doctor believed to have helped the CIA track down the deceased al Qaeda leader Osama bin Laden - architect of the 2001 attacks on the United States - has been accused of using a fake vaccination campaign to collect DNA samples.

Bin Laden was killed in a covert raid by U.S. special forces in 2011 in the Pakistani town of Abbottabad, where he was living, straining ties between the U.S. and Pakistan.

Pakistan sentenced alleged U.S. facilitator Dr. Shakil Afridi in 2012 to 33 years in jail on charges of belonging to militant group Lashkar-e-Islam, which he denies. That sentence was overturned but he remains in jail charged with murder relating to the death of a patient.