London: Pakistan, one of three countries with endemic polio, began an immunisation campaign this week in the city of Quetta for children under five after the discovery of a rare strain of the virus in sewage samples, officials said.
No cases of the rare 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.
Here are some more facts on polio:
Poliomyelitis, or polio, is a viral disease of the brain and spinal cord that can cause irreversible paralysis in a matter of hours.
There is no cure for polio, it can only be prevented. Polio vaccine, given multiple times, can protect a child for life. Vaccines can be oral or injected.
The virus is transmitted from person to person through the ingestion of faeces from contaminated hands, food or water.
Polio mainly affects children under five years of age. One in 200 infections leads to irreversible paralysis, usually in the legs.
Among those paralysed, 5 percent to 10 percent die when their breathing muscles become immobilised.
There were 35 reported polio cases at the end of 2016 compared with 350,000 cases in 1988.
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.
Immunisation efforts in Pakistan have in the past been hampered by Islamist militants who believed the campaigns were a cover for Western spies.
As long as one child remains infected, all children are at risk. If polio is not completely eradicated, 200,000 new cases each year could crop up within 10 years globally.