Influenzavirus B er kendt for kun at inficere mennesker og visse [[sæl]]arter, og giver disse [[influenza]].<ref name="pmid10807575">{{cite journal | author = Osterhaus AD, Rimmelzwaan GF, Martina BE, Bestebroer TM, Fouchier RA | title = Influenza B virus in seals | journal = Science | volume = 288 | issue = 5468 | pages = 1051–3 | year = 2000 | pmid = 10807575 | doi = 10.1126/science.288.5468.1051 }}</ref>
Dets afgrænsede evne til at inficere andre arter end de to førnævnte gør, at influenza B ikke er i stand til at skabe pandemier, som det ses ved [[Influenzavirus A]], hvis genom både kan mutere ([[antigen drift]]) og udveksles med andre virus ([[antigen skift]]).<ref name="pmid11779385">{{cite journal | author = Hay AJ, Gregory V, Douglas AR, Lin YP | title = The evolution of human influenza viruses | journal = Philos. Trans. R. Soc. Lond., B, Biol. Sci. | volume = 356 | issue = 1416 | pages = 1861–70 | year = 2001 | pmid = 11779385 | doi = 10.1098/rstb.2001.0999 | pmc = 1088562}}</ref><ref name="pmid15258979">{{cite journal | author = Matsuzaki Y, Sugawara K, Takashita E, Muraki Y, Hongo S, Katsushima N, Mizuta K, Nishimura H | title = Genetic diversity of influenza B virus: the frequent reassortment and cocirculation of the genetically distinct reassortant viruses in a community | journal = J. Med. Virol. | volume = 74 | issue = 1 | pages = 132–40 | year = 2004 | pmid = 15258979 | doi = 10.1002/jmv.20156}}</ref><ref name="pmid10196339">{{cite journal | author = Lindstrom SE, Hiromoto Y, Nishimura H, Saito T, Nerome R, Nerome K | title = Comparative Analysis of Evolutionary Mechanisms of the Hemagglutinin and Three Internal Protein Genes of Influenza B Virus: Multiple Cocirculating Lineages and Frequent Reassortment of the NP, M, and NS Genes | journal = J. Virol. | volume = 73 | issue = 5 | pages = 4413–26 | year = 1999 | pmid = 10196339 | doi = | pmc = 104222 }}</ref>
Yderligere udvikler influenza B vira sig langsommere end A vira og hurtigere en [[Influenzavirus C|C vira]].<ref name="pmid3267218">{{cite journal | author = Yamashita M, Krystal M, Fitch WM, Palese P | title = Influenza B virus evolution: co-circulating lineages and comparison of evolutionary pattern with those of influenza A and C viruses | journal = Virology | volume = 163 | issue = 1 | pages = 112–22 | year = 1988 | pmid = 3267218 | doi =10.1016/0042-6822(88)90238-3 }}</ref> Influenzavirus B muterer 2 til 3 gange mindre end [[influenzavirus A]].<ref>{{cite journal | author = Nobusawa E, Sato K | title = Comparison of the Mutation Rates of Human Influenza A and B Viruses | journal = J Virol | volume = 80 | issue = 7 | pages = 3675–8 | date = april 2006 | pmid = 16537638 | doi = 10.1128/JVI.80.7.3675-3678.2006 | pmc = 1440390}}</ref> Denne muterer dog så meget, at vedvarende immunitet ikke er mulig.
Videnskab Naturvidenskab Vira