FILE - An unidentified health official administers a polio vaccine to a child in Kawo Kano, Nigeria, April. 13, 2014.
FILE - An unidentified health official administers a polio vaccine to a child in Kawo Kano, Nigeria, April. 13, 2014.

As the world enters the final phase of a global polio eradication effort, French researchers have identified a mutant strain of the virus that is resistant to the polio vaccine. Despite this, an American expert said the war on polio can be won with continued vaccination.

Despite progress toward the goal of wiping polio off the face of the Earth with an aggressive child vaccination campaign, transmission of the paralytic illness continues in Nigeria, Pakistan and Afghanistan.

Now, a mutant strain of the virus responsible for a deadly outbreak in the Republic of the Congo in 2010 has been discovered, rendering the polio vaccine less effective.

Scientists at the French organization Institute of Research for Development, or IRD, found the mutant strain. They tested it on 60 blood samples from vaccinated volunteers in Congo and neighboring Gabon. Antibodies raised by the vaccine were found to be ineffective in neutralizing the virus in 15 to 30 percent of the samples.

The findings were published recently in the journal Proceedings of the National Academy of Sciences.

Walter Orenstein, associate director of the Emory Vaccine Center at Emory University in Atlanta, Georgia, is considered a world renowned expert in the field of infectious diseases and vaccination.  He said there is concern the virus may become more virulent.

“And there is the theoretical potential of evading the immune system. But I think the bottom line right now is what’s said in basically the last sentence of the paper, which said ..mass campaigns using oral polio vaccines stopped the outbreak,” he said.

But in some countries, there is violent opposition to those campaigns. Since January, attacks by the Taliban on vaccination teams in Pakistan and Afghanistan have resulted in 235 polio cases, a 15-year high.

The militants charge the healthcare workers are spies for Washington and the oral polio vaccine makes boys sterile.

Pakistani government officials, saying they don’t want to see children paralyzed for life, are vowing to make the country polio-free in six months. Orenstein said that’s the only way to lessen the threat of a vaccine-resistant strain.

“So it to me adds to the urgency of let’s just get rid of this virus, and then we won’t have to worry about this kind of issue,” he said.

Orenstein said it's likely polio will be eradicated in Africa by the end of this year, while Pakistan remains the major reservoir.

He said stepped-up commitments are needed to vanquish the disease once and for all.