Vaccine makers prep bird flu shot for humans 'just in case'; rich nations lock in supplies 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. Jennifer Rigby Reuters

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One current outbreak of avian flu known as H5N1 clade 2.3.4.4b has killed record numbers of birds and infected mammals. Human cases, however, remain very rare, and global health officials have said the risk of transmission between humans is still low.