From VOA Learning English, this is the Health Report.
Is a new deadly polio virus hiding somewhere in the world? Some scientists believe this might be true.
Polio causes paralysis, leaving victims unable to walk or move parts of their bodies. The disease does not usually kill.
But polio was deadly when the virus appeared in the Republic of the Congo in 2010.Nearly half of the 445 people who were infected died.
New research shows there might have been a weak spot in the polio vaccine. Reseachers say mutations, or changes, in the polio virus were responsible for that unusually deadly outbreak. The researchers say new kinds of polio may come into existence as the world gets closer to stopping the virus.
Felix Drexler is an expert on viruses at the University of Bonn in Germany. He says those infected in the Congo were different from other polio patients in an important way. He says about half of them rememberd taking three doses of the live vaccine. He says they should not have gotten sick as a result.
Mr Drexler and other researchers studied that polio virus. They found it had some never-before-seen mutations. These changes prevented disease-fighting antibodies from attacking the virus.
The Republic of the Congo had been polio free before the 2010 outbreak. It ended after four nationwide vaccination campaigns.
Experts say the worldwide end of polio is near. There have been fewer than 150 cases this year.
Walt Orenstein is with the Emory Vaccine Center in the United States. He says health workers need to kill the virus in the last few areas where it remains. Then, he says, talk about mutant strains or stronger vaccines would be unnecessary.