Old may be gold, according to the journal Proceedings of the National Academy of Sciences. The report states that the present TB vaccines are losing their efficiency in preventing tuberculosis, and scientists may do well to resurrect older versions of the vaccine.

The scientists led by Dr. Roland Brosch of the Institut Pasteur opine that modern BCG or bacillus Calmette Guerin vaccines used in immunization of 2 million children around the world weekly, are losing their power, probably due to changes in the genetic strains used.

The evolution of these strains and the subsequent loss of certain genes, are creating weaker immune reactions, note the scientists.

French scientists originally developed the BCG vaccine, which has been running for the last 90 years, in 1908. They managed to make a strain of tuberculosis (TB) less potent by growing it in a glycerin-potato mixture.

This meant when used in a vaccine it would produce an immune response without causing the actual disease. Once they found it was safe, they began to distribute the vaccine around the world.

Since the 1960s, there have been reports of the declining efficacy of the BCG vaccine.

A study in babies published in 2006 found that the early Japan strain prompted a stronger immune reaction than three newer strains that are used in 66% of modern immunizations.

Study leader, Dr Roland Brosch, senior researcher at the Institut says: "The earlier strains have undergone fewer genetic changes.