The creation of H5N1 bird flu strains that are transmissible between mammals has thrown the scientific community into a heated debate about whether such research should be allowed and how it should be regulated.
Four studies identify alternative origins for cells of the developing lymphatic system, challenging the long-standing view that they all come from veins.
Find the latest updates in this one-stop resource, including efficacy data and side effects of approved shots, as well as progress on new candidates entering human studies.