About the Authors: Katherine E. E. Johnson Affiliation: Center for Genomics & Systems Biology, Department of Biology, New York University, New York, New York, United States of America ORCID http://orcid.org/0000-0002-9226-0672 Timothy Song Affiliation: Center for Genomics & Systems Biology, Department of Biology, New York University, New York, New York, United States of America ORCID http://orcid.org/0000-0001-6932-0916 Benjamin Greenbaum Affiliation: Tisch Cancer Institute, Departments of Genetics and Genomics, Medicine, Oncological Sciences, and Pathology, Icahn School of Medicine of Mt Sinai, New York, New York, United States of America Elodie Ghedin * E-mail: elodie.ghedin@nyu.edu Affiliations Center for Genomics & Systems Biology, Department of Biology, New York University, New York, New York, United States of America, Department of Epidemiology, College of Global Public Health, New York University, New York, New York, United States of America ORCID http://orcid.org/0000-0002-1515-725XCitation: Johnson KEE, Song T, Greenbaum B, Ghedin E (2017) Getting the flu: 5 key facts about influenza virus evolution. Influenza A appears to be evolving under pressure to avoid CpG-containing oligonucleotides, possibly due to innate immune recognition, in a manner less present in influenza B evolution 21, 22. ...influenza B lineages have been shown to have lower rates of antigenic drift when compared to influenza A subtypes 23. ...the intrinsic diversity and loose transmission bottlenecks in circulating influenza populations can facilitate an increase in pathogenesis by allowing viral variants to cooperate with one another or by increasing the number of beneficial mutations appearing in cocirculating clones. Effective vaccination strategies would require a better understanding of the complex interplay of multivariant transmission dynamics, inter- and intrahost viral evolution, and the interaction of diverse strains with the host immune system.