After an uncommonly subdued 2011-2012 influenza season (see CDC: The Close Of A Mild Season), and a summer that featured an unprecedented number of variant swine flu infections (see An Increasingly Complex Flu Field) in the United States, no one is quite sure what to expect with the coming flu season.
Invariably, the word most often used by researchers when describing influenza is `unpredictable’.
Nevertheless, in order to come up with a vaccine each year, scientists must decide – 6 months in advance – what flu strains they think will be most active in the season ahead.
After 3 years with essentially no changes, this year’s flu vaccine formulation makes alterations to both the H3N2 and B virus strains.
- The H1N1 component remains essentially unchanged, with the A/California/7/2009 (H1N1)pdm09-like still recommended.
- The old A/Perth/16/2009 (H3N2)-like virus now gives way to the A/Victoria/361/2011 (H3N2)-like virus.
- And the Victoria lineage B/Brisbane/60/2008-like virus will be replaced by a Yamagata strain; the B/Wisconsin/1/2010-like virus.
The addition of these two new strains makes getting the vaccine this year all the more important, as community immunity to these recently emerging strains is likely low.
The vaccine die having been cast, each fall we monitor influenza activity around the world via a number of reporting tools, including:
- The World Health Organization’s bi-weekly global influenza update based on `data sources, including FluNet (reported by the Global Influenza Surveillance and Response System) and influenza reports from WHO Regional Offices and Member States.’
- The WHO/Europe influenza surveillance reports, which are released on a weekly basis.
- The ECDC provides both their Weekly Influenza Surveillance Overview (WISO) along with their periodic, highly detailed Influenza virus characterisation reports
- Canada releases a weekly FluWatch report.
- And the CDC produces a detailed FluView report each week.
There others, of course.
Combined, these resources provide us with a pretty good - albeit `backwards looking’ - overview of flu activity. At least in North America, Europe, and parts of the Pacific Rim.
Note: There are plenty of areas around the world where surveillance and reporting are lacking, and so we still run the risk of being blindsided by an emerging influenza strain.
During flu season I try to provide links, and highlights, to many of these flu surveillance reports each week. For now, flu activity around the world is low, but there are signs it may be increasing.
From yesterday’s WHO Flu report:
• Many countries of the Northern Hemisphere temperate region reported increasing detections of influenza viruses, particularly in North America and Western Europe, however none have crossed their seasonal threshold for ILI/ARI consultation rates.
• Several countries in the tropical areas experienced active transmission of influenza virus in recent weeks. In the Americas, Nicaragua and Costa Rica reported mainly influenza B virus detections. In Asia, India, Sri Lanka, Nepal, and Cambodia are all reporting a mixture of all three virus subtypes.
• In Sub-Saharan Africa, Cameroon and Ethiopia have reported an increase in influenza virus detections.
• Influenza activity in the temperate countries of the Southern Hemisphere is at inter-seasonal levels. A review of the 2012 southern hemisphere influenza season was published in the Weekly Epidemiological Record (WER) 2 November 2012, vol. 87, 44 (pp. 421–436)
Weekly reporting on influenza surveillance for the 2012–13 season started in week 40/2012 in Europe.
• In week 44/2012, all 26 reporting countries experienced low intensity of clinical influenza activity.
• Of 279 sentinel specimens tested across 19 countries, only two were positive for influenza virus.
• No hospitalised laboratory-confirmed influenza cases were reported.
Five weeks into the surveillance season for influenza, there has been no evidence of sustained influenza virus transmission in EU/EEA countries.
The story is pretty much the same in Canada, as we learn from their latest FluWatch Report.
Overall Influenza Summary
- Influenza activity in Canada increased slightly compared to the previous week; however overall activity still remains fairly low, with most regions of the country reporting no activity.
- In week 44, a total of 64 laboratory detections of influenza were reported; of which 91% were for influenza A viruses [71% A(H3) and 29% A(un-subtyped)].
- Six influenza outbreaks in long-term care facilities were reported in week 44.
- Eleven influenza A-associated hospitalizations were reported in week 44: 8 in adults >20 years of age, and 2 in children.
- The ILI consultation rate increased in week 44 to 21.9 per 1,000 patient visits but is within the expected level for this time of year.
In the United States, the CDC’s FluView Reports the beginnings of limited flu activity around the country:
During week 44 (October 28-November 3, 2012), influenza activity increased in some areas, but overall was similar to activity last week in the United States.
- Viral Surveillance: Of 3,277 specimens tested and reported by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories during week 44, 227 (6.9%) were positive for influenza.
- Pneumonia and Influenza Mortality: The proportion of deaths attributed to pneumonia and influenza (P&I) was slightly above the epidemic threshold.
- Influenza-associated Pediatric Deaths: No influenza-associated pediatric deaths were reported.
- Outpatient Illness Surveillance: The proportion of outpatient visits for influenza-like illness (ILI) was 1.3%, which is below the national baseline of 2.2%. All 10 regions reported ILI below region-specific baseline levels. One state experienced low ILI activity; New York City and 49 states experienced minimal ILI activity, and the District of Columbia had insufficient data.
- Geographic Spread of Influenza: The geographic spread of influenza in 1 state was reported as regional; 8 states reported local activity; the District of Columbia and 33 states reported sporadic activity; Guam and 8 states reported no influenza activity, and Puerto Rico and the U.S. Virgin Islands did not report.
Many years, influenza doesn’t begin to really spread until December or even January, so the level of activity we are seeing today is probably a poor prognosticator of what we will be seeing two or three months from now.
Influenza, however, is notoriously unpredictable. Which makes each flu season unique, and worthy of our attention.