Afghan women wait to receive polio vaccination for their children at a clinic on the outskirts of Herat on March 11, 2013. A new strategy for ending polio worldwide aims to boost security for violence-plagued vaccine workers and halt all polio outbreaks by the end of next year, global health authorities said Tuesday

A new strategy for ending polio worldwide aims to boost security for violence-plagued vaccine workers and halt polio outbreaks by the end of next year, global health authorities said Tuesday.

The latest plan to eradicate polio, endorsed by the World Health Organization, is designed to capitalize on momentum against the crippling disease and formally declare all parts of the world polio-free by 2018.

But threats against vaccine workers in Nigeria and Pakistan remain a key concern, as does raising the $5.5 billion needed for the next six years of work, said experts.

"We want it funded up front," said John Sever, vice chair of the International PolioPlus Committee at Rotary International, explaining that funding gaps have interrupted vaccination efforts in the past.

Polio, once a worldwide scourge, is endemic in just three countries now, and those that remain -- Afghanistan, Nigeria and Pakistan -- are "on a trajectory to interrupt transmission by the end of 2014," the Global Polio Eradication Initiative said in a statement.

"This will hold true if trends continue and current security challenges do not cause a prolonged or increased impact on operations."

Despite recent lethal attacks on vaccine stations in Nigeria and Pakistan, those two countries and Afghanistan all made progress in vaccinating more people and reducing polio cases to their lowest level ever in 2012.

Last year there were just 223 polio cases worldwide compared to 650 in 2011.

Hamid Jafari, director of polio operations and research at the World Health Organization, said experts prefer to bring an end to polio, rather than limit the number of cases each year.

"We have learned the hard way many times over it is not something that can be controlled easily. The cost of control at 223 cases a year would then indefinitely be about a billion dollars a year."

World health officials first set out to tackle polio in 1988, when endemic wild poliovirus afflicted more than 125 countries and more than 350,000 children were paralyzed for life by it every year.

Health workers trying to vaccinate people have come under fire from extremists who have killed 30 people in Nigeria and Pakistan in recent months.

Often, violence is fueled by rumors that the vaccine aims to sterilize Muslims, or that it is a cover for espionage by the West.

Boosting security at vaccine stations, holding shorter and lower profile campaigns, working with Islamic community leaders to spread the word about the need for polio vaccination and stressing the neutrality of health workers are part of the plan to protect vaccine efforts.

"I think the important message here is that the answers have to come from the communities themselves," said Rebecca Martin, director of the Global Immunization Division of the US Centers for Disease Control and Prevention.

An emphasis on routine immunization is another key part of the effort, said Apoorva Mallya, vaccine delivery program officer at the Bill and Melinda Gates Foundation where the plan was unveiled Tuesday.

"There is a need to sustain the gains. We have already interrupted wild virus in many places, India being the latest example, and we need to protect those gains," he said.

A major shift foreseen in the strategy is eliminating use of the oral vaccine that contains live poliovirus, because it can cause rare outbreaks, and replacing it with an inactivated virus that is delivered by a shot instead.

The strategy calls for that change to be complete by 2019 or 2020. However, the oral vaccine costs about 20 cents, compared to the inactivated vaccine given by shot, which can cost around $3 per dose.

Once wild poliovirus is no longer a danger and the vaccine-associated types disappear too, world governments may decide to stop vaccinating their populations altogether, possibly around 2025, experts said.

"As with smallpox, we would no longer have to vaccinate our children," said Sever. "So there is a financial savings forever, plus the benefit to mankind."