* Taliban attacks, vaccine ban leave many children exposed
* With polio virus circulating, disease taking hold again
* Dozens of children paralysed in Waziristan outbreak
* Dramatic progress towards wiping out polio in jeopardy
By Kate Kelland, Health and Science Correspondent
LONDON, Oct 18 (Reuters) - A Taliban ban on vaccination is exacerbating a serious polio outbreak in Pakistan, threatening to derail dramatic progress made this year towards wiping out the disease worldwide, health officials say.
Health teams in Pakistan have been attacked repeatedly since the Taliban denounced vaccines as a Western plot to sterilise Muslims and imposed bans on inoculation in June 2012.
In North Waziristan, a region near the Afghan border that has been cordoned off by the Taliban, dozens of children, many under the age of two, have been crippled by the viral disease in the past six months.
And there is evidence in tests conducted on sewage samples in some of the country's major cities that the polio virus is starting to spread beyond these isolated pockets and could soon spark fresh polio outbreaks in more densely populated areas.
"We have entered a phase that we were all worried about and were afraid might happen," Elias Durry, head of the Global Polio Eradication Initiative (GPEI) in Pakistan, told Reuters in a telephone interview.
"The risk is that as long as the virus is still circulating, and as long as we have no means of reaching these children and immunising them to interrupt virus transmission, it could jeopardise everything that has been done so far - not only in Pakistan, but also in the region and around the globe."
CORNERING THE VIRUS
Polio is a highly infectious disease that invades the nervous system and can cause irreversible paralysis in a matter of hours. A $5.5 billion global eradication plan was launched in April with the aim of vaccinating 250 million children multiple times each year to stop the virus finding new footholds, and stepping up surveillance in more than 70 countries.
The virus has been cornered to just a handful of areas in Nigeria, Afghanistan and Pakistan, the three countries where polio is endemic. Global cases have dropped by more than 99.9 percent in less than three decades, from 350,000 in 1985 to just 223 last year, according to the GPEI.
But so far in 2013, there have already been 296 cases worldwide. Forty-three were in Pakistan, the vast majority in children in the semi-autonomous Pashtun lands along the Afghan border known as the Federally Administered Tribal Areas (FATA), which include North Waziristan.
Accusations that immunisation campaigns are cover for spies were given credence when it emerged that the United States had used a Pakistani vaccination team to gather intelligence about al Qaeda leader Osama bin Laden, who was found and killed by U.S. special forces in Pakistan in 2011.
The Taliban ban, and associated security threats, mean the polio virus could easily escape and spread back into previously cleared areas.
Tariq Bhutta of the Pakistan Paediatric Association said there was little prospect that the militant Islamist group would change its stance. He said attacks on health teams attempting to reach children to immunise them were becoming both more frequent and more violent.
"The vaccination teams are still going out, but at risk to their lives," he told Reuters. "People can come up on motorbikes and shoot them, and they've also started attacking the police put there to protect the vaccination teams."
A Taliban bomb that exploded earlier this month near a polio vaccination team in the northwestern city of Peshawar killed two people and appeared to target police assigned to protect the health workers.
"This will only be solved if the polio teams can get access to those children - either inside FATA, or when the children move out into other areas," Bhutta said. "Without that I don't see how things can improve. Rather I think things might get more serious when the polio virus gets out into settled areas."
The GPEI says the FATA is the area with the largest number of children being paralysed by wild poliovirus in all of Asia.
Four polio cases in children in Pakistan were reported in the last week. Because the virus spreads from person to person, the World Health Organization says as long as any child remains infected, children everywhere are at risk.
(Editing by Mark Trevelyan)