Public health officials plotting the strategy behind the effort to rid the world of polio are seeking approval for fundamental changes to the blueprint for the way the eradication program will eventually come to a stop.

The Global Polio Eradication Initiative is asking for endorsement of changes it wants to make to the polio endgame, the tricky manoeuvring that will be needed to safely stop vaccinating against polio once it appears the viruses are no longer spreading and causing disease.

The initiative hopes the options it is proposing will speed up the end of polio transmission and make the final moves in this lengthy battle safer.

At a meeting in Geneva today, it is asking the World Health Organization's vaccine experts -- the Strategic Advisory Group of Experts on Immunization -- to approve recommendations aimed at making injectable polio vaccine a more crucial component of the endgame strategy.

Getting a green light from the committee, which goes by the acronym the SAGE, is only the first step in an approval process that would require countries to sign on as well. And the WHO's point person for polio knows all countries aren't there yet when it comes to agreeing to a role for injectable vaccine, or IPV as it is known.

"I think we have to accept that we are not at a point yet where every country has concurred to introduce this universally. Not at all," Dr. Bruce Aylward, the assistant director-general for polio, emergencies and country collaboration said in a recent interview.

Since the polio eradication program was launched in 1988 it has relied on oral polio vaccine. OPV, in polio shorthand, costs pennies a dose and is easy to administer. Anyone can be trained to give the vaccine, two drops of which are squeezed from a eye dropper into an open mouth. It is given to millions of children in scores of countries every year.

By comparison, the injectable vaccine is substantially more expensive, currently running at around $2.75 a dose when procured through UNICEF, which buys in bulk for developing countries. (Children immunized with injectable vaccine need three or four doses each.)

And the $2.75 is just the cost of the vaccine. Factor in the syringes and the medical professionals needed to wield them, and it becomes clear why for many years IPV was only used by well-to-do countries. Of late, though, an increasing number of middle-income countries have been using it as well.

That's because despite its higher price, IPV is safer than the oral vaccine, which is made from live but weakened polio viruses.

OPV causes polio in a small portion of children who get the vaccine or encounter the viruses used in the serum. It is estimated that one out of every 750,000 children will develop polio after getting their first dose of OPV. That is called vaccine-associated paralytic polio or VAPP.

And the vaccine viruses, which inoculated children shed in their stools, can spread in an environment where sanitation is poor, moving from vaccinated child to unvaccinated child in tainted water or tiny bits of fecal matter picked up on a finger that finds its way into a mouth. If those vaccine viruses spread long enough, they regain their power to paralyze, acting like regular polio viruses. Polio cases caused by spreading vaccine viruses are called VDPVs -- vaccine-derived polio viruses.

When wild polio viruses paralyzed scores of thousands of children a year, the benefits of oral vaccine over rode the risks of VAPP and VDPV cases.

But so far this year there have only been 177 cases of paralytic polio, in four countries. When the world gets down to a few dozen of cases of polio a year, the continued heavy reliance on OPV will risk seeding the world with vaccine viruses that could spread and trigger outbreaks of VDPV cases.

In essence, the question is: When is it no longer safe to fight fire with fire?

Some experts have been saying for years that injectable vaccine has to play a role in the phasing out of oral vaccine. And for years the polio campaign leadership resisted those calls, saying the scientific evidence was not there to support the move.

These days, though, they are IPV converts. And they are asking the SAGE to urge that all countries vaccinate all vulnerable children with at least one dose of injectable vaccine as part of the endgame strategy. The thinking is that if vaccine viruses start spreading more broadly in the phasing out of the oral vaccine, children will have some protection from the dose of IPV.

Aylward suggested an outbreak of vaccine-derived polio in Nigeria that started in 2005 has shaped thinking about the risk vaccine viruses pose. So far there have been 381 cases of paralytic polio in that outbreak, which has not yet been extinguished.

"There's increasing evidence that these things are real. They can persist and take some time to knock out. And Africa may be at the greatest risk due to the gaps in immunization coverage there," he said. It's know that vaccine viruses spread best in areas where the percentage of children who are fully immunized is low.

But 24 years into the eradication effort, many countries are eager to stop spending money on polio vaccination entirely. Earlier this year, in fact, Bangladesh debated whether it could cut its national immunization day, a cornerstone of polio control efforts. (The government was urged not to and it followed the advice.)

Aylward said the polio campaign partners are working hard to find a way to get the price of injectable vaccine below $1 a dose and ideally closer to 50 cents a shot. At that rate, more countries would buy into the IPV plan, he said.

Options on the table include using a smaller dose but injecting it into the skin, rather than the muscle, because that triggers a better immune response, or using a boosting compound called an adjuvant with the vaccine to allow for smaller doses.

"The issue now is making sure that there are affordable products available but then also that countries will accept to do that," Aylward said. "Because there are a lot of countries that wish they could just stop OPV cold."

The polio eradication campaign is a partnership of Rotary International, the WHO, UNICEF, the U.S. Centers for Disease Control and the Bill and Melinda Gates Foundation.

It currently hopes to halt the spread of polio in the three countries which have never stopped transmission -- Nigeria, Pakistan and Afghanistan -- by 2014-15. (The fourth country to report cases this year is Chad, which has seen sporadic importations of polio from Nigeria.) If that goal is reached, the world would be declared polio free three years after the last case occurred.