Influenza Activity — United States and Worldwide, May 19–September 28, 2019, and Composition of the 2020 Southern Hemisphere Influenza Vaccine

Scott Epperson, DVM; C. Todd Davis, PhD; Lynnette Brammer, MPH; Anwar Isa Abd Elal; Noreen Ajayi, MPH; John Barnes, PhD; Alicia P. Budd, MPH; Erin Burns, MA; Peter Daly, MPH; Vivien G. Dugan, PhD; Alicia M. Fry, MD; Yunho Jang, PhD; Sara Jo Johnson, MPH; Krista Kniss, MPH; Rebecca Kondor, PhD; Lisa A. Grohskopf, MD; Larisa Gubareva, PhD; Angiezel Merced-Morales, MPH; Wendy Sessions, MPH; James Stevens, PhD; David E. Wentworth, PhD; Xiyan Xu, MD; Daniel Jernigan, MD


Morbidity and Mortality Weekly Report. 2019;68(40):880-884. 

In This Article

Antiviral Resistance of Influenza Viruses

CDC tested 812 influenza virus specimens collected during May 19–September 28 from the United States and worldwide for resistance to oseltamivir, peramivir, and zanamivir. All but two of the viruses tested (245 influenza A(H1N1)pdm09 viruses [161 international and 84 U.S. viruses], 406 influenza A(H3N2) viruses [284 international and 122 U.S.], and 161 influenza B viruses [71 international and 90 U.S.]) were susceptible to these influenza antiviral medications. One (0.1%) influenza A(H1N1)pdm09 virus contained the H275Y amino acid substitution in the neuraminidase and exhibited highly reduced inhibition by oseltamivir and peramivir, and one (0.1%) influenza B virus contained the amino acid substitution I221T and exhibited reduced inhibition by the same two neuraminidase inhibitors. Among 824 influenza virus specimens (253 A(H1N1)pdm09, 406 A(H3N2) and 165 type B assessed for susceptibility to baloxavir, one (0.1%) A(H3N2) virus contained amino acid substitution I38L in the polymerase acidic (PA) protein, which was previously associated with at least a threefold decreased baloxavir susceptibility. High levels of resistance to the adamantanes (amantadine and rimantadine) persisted among influenza A(H1N1)pdm09 and influenza A(H3N2) viruses, which is consistent with the current recommendation to avoid use of these medications against influenza. Influenza antiviral recommendations are available at https://www.cdc.gov/flu/professionals/antivirals/links.htm.