Family clusters have happened for a long time with H5N1, with human-to-human being likely. For instance a paper that currently goes around from 2007: https://ww

Family clusters have happened for a long time with H5N1, with human-to-human being likely. For instance a paper that currently goes around from 2007: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2857285/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2857285/ The issue is that each mammal/human infection gives the virus the possibility to adapt to mammals/humans and/or reassortment with other influenza viruses, like happened with H1N1/09.