The World Health Organization has published their latest global flu surveillance report, current as of March 20th, that likely represents the peak of the Northern Hemisphere's 2015-16 flu season. Despite reports of heavy flu activity in Russia and Eastern Europe, the United States and Canada appear to have escaped with mild to moderate seasons.
As flu starts to recede in the Northern Hemisphere we look for it to begin to increase over the next few months in the Southern Hemisphere, and already we've seen some early reports of flu in Brazil (see FluTrackers thread).
Although primarily a winter respiratory disease, in the tropics influenza transmits year-round, albeit at lower levels than at the higher latitudes (see Influenza Burden and Transmission in the Tropics).
Perhaps most uniquely, Hong Kong often sees a biphasic or `double peaked’ flu season, with heavy activity from February–April and again June through August , as described in the 2008 PLoS One research paper Seasonality of Influenza A(H3N2) Virus: A Hong Kong Perspective (1997–2006).
Due to its much larger population, the Northern Hemisphere's flu season is often viewed as more likely to produce new influenza variants, but the truth is flu's evolution continues someplace in the world year-round.
So we'll watch the upcoming flu seasons in Brazil, Argentina, Australia, New Zealand, South Africa . . . and even Hong Kong . . . with interest.
Meanwhile, here is the latest WHO global flu summary.
Influenza update - 26004 April 2016, - Update number 260, based on data up to 20 March, 2016
Globally, elevated levels of influenza activity continued to be reported in North America, in parts of Europe and in Northern Temperate Asia. An increase in influenza B virus activity has been reported in Northern Temperate Asia, South East Asia and Europe.
- In North America, influenza activity has peaked and remained elevated with influenza A(H1N1)pdm09 virus predominating. Canada reported increased detections of influenza B virus.
- In Europe, high level of influenza activity was still reported with increasing detections of influenza B virus. In most countries influenza activity seemed to have peaked.
- Northern Temperate Asia continued to report ongoing and elevated levels of influenza with increasing proportions of influenza B.
- In western Asia, influenza activity continued to decline as seen in previous reporting weeks.
- In Central America and the Caribbean, Jamaica reported elevated SARI activity associated with influenza A(H1N1)pdm09 virus infection. High influenza activity due to influenza A(H1N1)pdm09 was reported in Guatemala.
- In tropical South America, influenza activity in Brazil continued to remain high with influenza A(H1N1)pdm09 predominating. Elevated SARI activity associated with respiratory syncytial virus (RSV) infection was reported in Ecuador.
- In the temperate countries of the Southern Hemisphere influenza virus activity remained low.
- National Influenza Centres (NICs) and other national influenza laboratories from 89 countries, areas or territories reported data to FluNet for the time period from 07 March 2016 to 20 March 2016 (data as of 2016-04-01 04:47:34 UTC).The WHO GISRS laboratories tested more than 138525 specimens during that time period. 40448 were positive for influenza viruses, of which 24973 (61.7%) were typed as influenza A and 15475 (38.3%) as influenza B. Of the sub-typed influenza A viruses, 10087 (87.5%) were influenza A(H1N1)pdm09 and 1442 (12.5%) were influenza A(H3N2). Of the characterized B viruses, 862 (18.3%) belonged to the B-Yamagata lineage and 3836 (81.7%) to the B-Victoria lineage.
Detailed influenza update