Update: Influenza Activity — United States and Worldwide, May 20–October 13, 2018

Eric J. Chow, MD; C. Todd Davis, PhD; Anwar Isa Abd Elal; Noreen Alabi, MPH; Eduardo Azziz-Baumgartner, MD; John Barnes, PhD; Lenee Blanton, MPH; Lynnette Brammer, MPH; Alicia P. Budd, MPH; Erin Burns, MA; William W. Davis, DrPH; Vivien G. Dugan, PhD; Alicia M. Fry, MD; Rebecca Garten, PhD; Lisa A. Grohskopf, MD; Larisa Gubareva, PhD; Yunho Jang, PhD; Joyce Jones, MS; Krista Kniss, MPH; Stephen Lindstrom, PhD; Desiree Mustaquim, MPH; Rachael Porter, MPH; Melissa Rolfes, PhD; Wendy Sessions, MPH; Calli Taylor, MPH; David E. Wentworth, PhD; Xiyan Xu, MD; Natosha Zanders, MS; Jacqueline Katz, PhD; Daniel Jernigan, MD


Morbidity and Mortality Weekly Report. 2018;67(42):1178-1185. 

In This Article


CDC serves as the WHO Collaborating Center for Surveillance, Epidemiology, and Control of Influenza, one of six WHO Collaborating Centers for Influenza in the WHO Global Influenza Surveillance and Response System (GISRS).††† CDC, along with other international public health partners, provides surveillance and virus characterization data to WHO. The timing of influenza activity and the predominant circulating virus around the world can vary by region.§§§ Overall, reported Southern Hemisphere influenza activity has been relatively low and fairly mild, with influenza A(H1N1)pdm09 viruses predominating in most regions.¶¶¶ Influenza data from GISRS during May 20–September 30 in temperate climate South American countries suggest that activity began to increase in mid-May and peaked in August. Influenza A(H3N2) predominated in Chile and Paraguay. In temperate Southern Africa, influenza activity increased in April and peaked in June, with A(H1N1)pdm09 predominating. A second wave of elevated activity in Southern Africa of mostly influenza B began in late August and peaked in September. Influenza activity in Australia and New Zealand was below seasonal threshold with A(H1N1)pdm09 predominating. Influenza activity in regions with more tropical climates (Central America and the Caribbean, tropical South America, Southern Asia, and Southeast Asia) was more variable, but A(H1N1)pdm09 virus predominated in most countries. Influenza A(H1N1)pdm09, A(H3N2), and B viruses cocirculated in Eastern Africa, and influenza A(H1N1)pdm09 and A(H3N2) viruses cocirculated in Southern Asia.

††† http://www.who.int/influenza/gisrs_laboratory/collaborating_centres/en.
§§§In temperate climates, the onset and peak of influenza activity might vary substantially from one influenza season to the next, but generally begins to increase in the late fall. In the Northern Hemisphere's temperate regions, annual epidemics of influenza typically occur during October–February, but the peak of influenza activity can occur as late as April or May. In temperate regions of the Southern Hemisphere, influenza activity typically peaks during May through August. Although temperate regions of the world experience a seasonal peak in influenza activity, influenza viruses can be isolated year-round. The timing of seasonal peaks in influenza activity in tropical and subtropical countries varies by region. Multiple peaks of activity during the same year have been seen in some areas and influenza infection can occur year-round.
¶¶¶ http://www.who.int/influenza/surveillance_monitoring/updates/en/.