# 6393
As previously mentioned in this blog (see Hong Kong: Flu Activity Continues To Rise), while influenza activity in most the Northern Hemisphere (excluding the tropics) is practically non-existent right now, Hong Kong continues to see an unusual level of flu activity.
Today, the Hong Kong government released a brief statement suggesting that a `genetic change’ to the flu virus circulating in Hong Kong may be behind this season’s persistence.
While this may sound a bit ominous, there may be less to this story than it first suggests.
We’ve been aware of small, antigenic changes occurring in the H3N2 flu virus for a number of months now, a trend which prompted a change to next fall’s flu vaccine (see WHO: Northern Hemisphere 2012-2013 Flu Vaccine Composition).
Unfortunately, today’s story provides no real detail on the `genetic changes’ being observed in Hong Kong, making it difficult to draw any comparisons to the antigenic changes seen elsewhere.
First the news statement from NEWS.GOV.HK, then I’ll be back with a little more.
Flu season may be longer
June 18, 2012
A genetic change of virus may lengthen this year's peak flu season. Centre for Health Protection Controller Dr Thomas Tsang issued the warning today, saying the flu pattern this year is unusual.
Local influenza activity remained high from January to June. From the last week of May to the first week of June there were 1,100 flu cases.
The number of influenza detections dropped to about 600 last week, but is still high compared with the average of 100 cases per week in recent years.
He said the flu strain this year has changed slightly in genetic make up.
More than 170 people have died of influenza since January, 90% of them being elderly, Dr Tsang said, urging the public and institutions to be alert as the school holidays approach.
About 30 enterovirus infections are being reported in childcare centres every week, he added, including seven serious cases.
Flu viruses are constantly changing and evolving, and so minor changes to the virus are to be expected. Over time enough changes can accrue that they change the behavior or activity of the virus.
Late last month, in a letter to doctors, the Centre For Health Protection mentioned that the seasonal H3N2 virus being seen in Hong Kong had drifted away from the vaccine strain.
An excerpt from that letter reads:
The current circulating influenza A(H3N2) virus is antigenically related but not identical to the current vaccine strain, A/Perth/16/2009 (H3N2)-like virus.
Separately, the circulating influenza B viruses belonged to two lineages, the Victoria and Yamagata lineage.
The latest laboratory data showed that the Yamagata lineage accounts for around 70-80% of the circulating influenza B viruses. As compared with influenza B viruses of Victoria lineage, influenza B viruses of the Yamagata lineage are antigenically less similar to the current vaccine strain B/Brisbane/60/2008-like virus. Though the match is less than optimal, studies have demonstrated some degree of cross protection with the available influenza vaccine against current circulating strains.
The most recent Flu Express report from the CHP (June 14th) indicates that by far, the bulk of the flu activity being detected right now are seasonal H3.
While this year’s flu season in Hong Kong remains atypical, the good news is, that there is probably no place on the planet better equipped to analyze changes to the flu virus than Hong Kong.
Hopefully we’ll get a more detailed report on what these `genetic changes’ might be in the near future.
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