# 4749
A trend we’ve been watching for the past several months has been the persistence of seasonal H3N2 influenza in some regions of the world.
The latest WHO update (week 26 – ending July 3rd) highlights the mixtures of laboratory typed flu strains from several reporting countries.
As you can see, H3N2 continues to circulate in Mexico, Brazil, Argentina, South Africa, Australia, and parts of South East Asia.
Today we’ve a report (h/t Tetano on FluTrackers) from Singapore indicating that 45% of positive flu samples are coming back as H3N2.
Fri, Jul 23, 2010
By Kenny Chee
THE Influenza A (H1N1) viral strain is no longer the dominant flu virus here, Singapore's Ministry of Health said yesterday.
And, since the strain has been found to be in the process of becoming seasonal in nature, Singapore and other Asean countries have stepped down, or are stepping down, their pandemic alert levels, said Health Minister Khaw Boon Wan.
The Health Ministry said that, as of last week, Influenza A (H1N1) comprised 31 per cent of all flu cases in the community here. But it is no longer the main circulating flu strain in Singapore, as it was as late as in May.
The seasonal strains, Influenza A (H3N2) and Influenza B, now constitute 45 per cent and 24 per cent of flu cases here, respectively.
In the last week of May, H1N1 accounted for 50 per cent of circulating strains, with the rest made up of H3N2 and Influenza B.
Given the past history of pandemics, the future of H3N2 was in serious doubt a few months ago.
In 1918, 1957, and again in 1968, the newly emerging pandemic strain managed to completely supplant the previously circulating A strains.
In 1977, however, the H1N1 virus reappeared after a 20 year absence – possibly due to an accidental laboratory release in the Soviet Union – and for the first time in modern history we had two influenza A strains (H3N2 and H1N1) in co-circulation.
Unlike novel H1N1, which largely spared the elderly over the past year, H3N2 has traditionally never been a respecter of age. Years when H3N2 dominated have often produced more severe flu seasons.
Last year an antigenic change was detected in the H3N2 virus that may make prior exposure and/or vaccination less protective.
This fall’s vaccine has been reformulated to include antigens to this new strain.
Vaccination, while not 100% perfect, remains your best protection against the flu each year.
The future of H3N2, the mixture of flu viruses this fall, and the severity and impact of the upcoming flu season are far from certain at this date.
Influenza is notoriously unpredictable, and we still appear to be in bit of a transition period. One where the eventual viral winners and losers have yet to be sorted out.
Regardless of what the World Health Organization decides on the status of the 2009 pandemic, this fall ought to provide us with ample opportunities to learn more about the evolution and spread of influenza viruses.
So stay tuned.
