TB vaccines can vary greatly, study finds. But does that mean some are less protective?

It all started with a bit of bacteria swiped from the udder of a tuberculous French cow. Initially, it was just another livestock sample, a speck of virulence lounging in a Paris lab. But then it began to change. Two scientists had brought some of it to Lille, near the Belgian border, and had fed it a concoction of potato, glycerin, and ox bile. The bugs liked this witches’ brew, and multiplied, and multiplied again.