Scientists confirm it only takes 3 amino acid mutations to switch the receptor specificity of the H7N9 influenza virus from avian to human-type, making it similar to the 2009 H1 flu pandemic virus. Due to the risks, the scientists were not allowed to test these mutations in live animals.

See the source article by following the link below:
Scientists confirm it only takes 3 amino acid mutations to switch the receptor specificity of the H7N9 influenza virus from avian to human-type, making it similar to the 2009 H1 flu pandemic virus. Due to the risks, the scientists were not allowed to test these mutations in live animals.