LONDON, March 20 (Reuters) - Some of the world's leading makers of flu vaccines say they could make hundreds of millions of bird flu shots for humans within months if a new strain of avian influenza ever jumps across the species divide. agency said it has signed legally binding agreements with 14 manufacturers for 10% of their pandemic flu vaccine “as it comes off the production line", in a mix of donated doses and doses to be bought by the agency at an affordable price. The results will be closely watched, as the data on Moderna’s seasonal flu candidate was mixed