# 5235
In striking contrast to North America – which is seeing primarily the H3N2 influenza strain - Europe is dealing with a return of the 2009 (formerly pandemic) H1N1 strain.
You can find the most recent U.S. and Canadian weekly surveillance data here, and the World Health Organization’s latest global surveillance report here.
Today, a look at the ECDC’s weekly surveillance report for Europe, which you may read in full here.
A summary, and some excerpts, followed by a little discussion:
Main surveillance developments in week 1/2011 (03 –09 Jan 2011)
Most countries are now reporting regional or widespread influenza activity, with medium to high influenza-like illness/acute respiratory infection (ILI/ARI) consultation rates and increasing trends. This is more prominent in Western European countries.
- Forty-three per cent of sentinel swabs tested positive for influenza: 71% were type A, and of the type A viruses subtyped, 97% were A(H1N1) 2009.
- Since week 40/2010, 1148 severe acute respiratory infection (SARI) cases, including 37 fatal cases, have been reported by seven countries.
- In addition to the UK, other countries are now reporting cases requiring higher level care and deaths in young adults associated with influenza infection. Most are with A(H1N1) 2009 virus, but some are with B viruses as well.
Sentinel surveillance of ILI/ARI: In addition to Denmark, Ireland and the UK (England) that had reported high ILI/ARI consultation levels the previous week, Norway has changed its indicator from medium to high.
In North America, roughly 90% of the influenza A viruses identified in recent weeks have been A/H3N2, while in Europe the opposite is true; in the latest report 97% were A/H1N1.
- Years when A/H3N2 dominates are generally more severe, particularly among those over the age of 65
- While mostly producing mild symptoms, novel A/H1N1 can produce severe illness, and has a predilection for younger adults and children.
Illustrating the great difficulty (some might even say `folly’) in trying to choose, months in advance, which groups to preferentially target for influenza vaccination.
Complicating matters, the strains in circulation in North America and Europe are hardly static. With roughly three months left to the flu season, H1N1 could yet see a resurgence on this side of the Atlantic, and H3N2 could still spark a second wave in Europe.
Welcome to the wildly unpredictable world of influenza.
Where even in this age of increased international travel and intermingling of people, the kind of flu season that North American and Europe end up seeing can still be oceans apart.
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