New York is still such a noisy city that its inhabitants could suffer from significant hearing loss in coming years, a study made public Wednesday has found.

Presented at a conference of the New York Academy of Medicine, the study found that 98 percent of noise measurements taken were at levels harmful to human health.

Fifteen countries in Africa are undertaking a mass polio immunization campaign for 72 million children this week, the World Health Organization said on Tuesday.

"This week Africa will be conducting a 15 country synchronized immunization campaign with oral vaccine," said Rod Curtis, a spokesman for the WHO in Geneva.

A new polio vaccine offers superior immunization and is raising hopes of a total eradication of the disease, according to a study published on Tuesday by British medical journal The Lancet.

There are three types of the polio virus, and while type 2 has been almost entirely eradicated since mass vaccinations began in 1988, types 1 and 3 remain a global health threat.

Scientists have shown for the first time that it may be possible to replace a human hip or knee with a joint grown naturally inside the body using the patient's stem cells.

In experiments on rabbits, the researchers coaxed the animals' stem cells to rebuild the bone and cartilage of a missing leg joint, according to a study published on Thursday.