The red band signifies the tropics, which has no distinct flu season. Viruses circulate there, at a low level, year round. – Credit Wikipedia
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While most of the Northern Hemisphere is basking in summer warmth and seeing very little flu activity (Hong Kong being an exception), it is winter south of the equator and flu season is well underway in Australia, New Zealand, and parts of South America and Africa.
Watching what happens during the flu season in the opposite hemisphere can sometimes give us clues as to what we might expect in the fall.
Of course, it doesn’t always prove predictive.
After the mildest flu season in memory in the Northern Hemisphere, it appears that Australia and New Zealand are getting hit harder, and earlier than usual.
First stop, a media report from the West Australian, then we’ll take a look at the latest surveillance data.
Pressure mounts with different flu virus
Peta Rasdien, The West Australian July 19, 2012, 7:39 am
The earliest start to the flu season in 10 years and the rise of a strain known to cause more severe illness is putting pressure on WA's already stretched health resources.
The `different’ flu virus is the seasonal H3N2 virus – which has antigenically drifted slightly away from the vaccine strain currently in use (see WHO: Southern Hemisphere 2012 Flu Vaccine Composition).
The existing vaccine contains the A/Perth/16/2009 (H3N2)-like virus, which is hoped to be at least somewhat effective against the evolving virus.
This fall, a new vaccine will be introduced that contains the updated A/Victoria/361/2011 (H3N2)-like virus (see WHO: Northern Hemisphere 2012-2013 Flu Vaccine Composition).
Historically, years where the H3N2 virus has been the dominant strain tend to produce worse flu seasons. The virus often hits harder than H1N1, and is more likely to target the elderly.
From New Zealand’s ESR Public Health Surveillance, we get these latest numbers in their Influenza Weekly Report 2012/28.
As you can see, the weekly consultations for ILI’s (Influenza-like Illness) are climbing like a homesick angel, and are running well ahead of the reports from the past 2 years.
While ILI activity in NZ is heavy, it does not reach the epidemic threshold (400 per 100K).
The week 28 report summary reads:
ILI through sentinel surveillance was reported from 19 out of 20 District Health Boards (DHB) with a national consultation rate of 102.8 per 100 000 (399 ILI consultations). A total of 905 swabs were received from sentinel (79) and non-sentinel (826) surveillance.
331 viruses were identified: A(H3N2) (232), A (Not subtyped) (35), A(H1N1)pdm09 (31), B (Lineage not determined) (26), A/Perth/16/2009 (H3N2)-like (5) and B/Wisconsin/1/2010-
like (2)
About 70% of the viruses identified were H3N2, while only 10% were the 2009 H1N1 strain.
The situation in Australia appears similar, although the latest surveillance numbers are not quite as current as what we have from New Zealand.
This from Australia’s Department of Health and Ageing.
Australian influenza report 2012 - Current report: No 2 - 9 June to 22 June 2012
Summary
- Across all surveillance systems, influenza activity has continued to increase this fortnight.
- All jurisdictions have reported increases in influenza detections above background levels, with South Australia, Victoria, New South Wales, the Australian Capital Territory and the centre of the Northern Territory reporting significant recent increases in activity.
- Influenza-like illness (ILI) activity has continued to increase, with the seasonal increase occurring slightly earlier than in previous years (excluding 2009).
- During this fortnight there were 2,233 laboratory confirmed notifications of influenza, almost double the number of notifications from the previous fortnight. New South Wales, Queensland and South Australia continue to report the highest number of notifications.
- Nationally, influenza A(H3N2) is the predominant circulating strain with some co-circulation of influenza B. Influenza A(H3N2) is predominant across most states and territories, however influenza B represents around 75% and 40% of all notifications in the Northern Territory and Western Australia, respectively. So far in 2012 there have been very few notifications of pandemic (H1N1) 2009.
- As at 22 June 2012, there have been 6,027 confirmed cases of influenza reported. Excluding 2009, notifications of influenza in 2012 have started their seasonal increase slightly earlier in comparison with previous years.
- Influenza associated hospitalisations have continued to increase this fortnight, particularly at the South Australian and Northern Territory sites. Overall, 40% of hospitalisations have been associated with influenza B infections, mostly reported from the Northern Territory. Amongst other jurisdictional sites, influenza A is more common.
- The WHO has reported that the influenza season has not yet started in the temperate countries of the southern hemisphere, although several countries, including Australia, Chile, Paraguay and South Africa have reported small but sustained increases of influenza virus detections. Influenza A(H3N2) viruses have been the most commonly detected in recent weeks in the southern hemisphere temperate region.
Based on this chart, this year’s ILI activity is off to the fastest start in Australia since the H1N1 pandemic of 2009.
As far as what the southern hemisphere’s flu season tells us about the fall flu season ahead?
Well, the old adage is that if you’ve seen one flu season, you’ve seen one flu season.
Influenza viruses are notoriously unpredictable, and flu seasons that span the globe, even more so. We won’t know what kind of flu season we are going to have until we’ve had it.
We will continue to watch the flu season evolve to our south, however, looking for any clues that might arise.
But whatever comes, we do have one advantage over our friends south of the border this year; the new flu shot with antigens expected to be more protective against the drifted H3N2 virus that will be available this fall.
Making getting the seasonal flu shot this fall all the more important this year.
Add in the routine practicing of good `flu hygiene’ (covering coughs, washing hands, staying home when sick), and you can substantially decrease you odds of getting the flu this coming winter.
