Photo Credit NIAID
# 8154
The ECDC publishes a periodic review of recently isolated flu viruses in the EU they call an Influenza Virus Characterization Report. The last one we looked at was in August (see ECDC: Influenza Virus Characterization – July 2013), and the news ;last summer was pretty good; the majority of the viruses analyzed still appeared to be antigenically similar to those in this year’s vaccine.
While flu season is going full steam in North America, flu reports from the EU indicate a much later start to the season. Additionally, while we are seeing a season heavily dominated by the pH1N1 virus, in Europe it is the H3N2 virus that leads the way.
While we talk about the four main strains of influenza that are currently circulating in humans (A/H1N1(pdm), A/H3N2, B Victoria, B Yamagata) as if they were single entities - in reality – within each strain, you will find a good deal of diversity. New `prototypes’ from these strains are constantly being generated (mostly by antigenic drift) and `field tested’ for biological fitness and transmissibility.
Most are evolutionary failures.
But since decisions regarding what strains to include in the next flu vaccine must be made 6 months in advance, it is important to detect any new `trends’ among the flu viruses in circulation. Which is why scientists must monitor these viruses constantly.
Today the ECDC has published a new influenza characterization report, that like the last one, finds most of the viruses tested still antigenically similar to the vaccine strains. But they do report several new H3N2 samples with specific HA amino acid substitutions, and that `antigenic characterization is pending’.
Here then is the summary of today’s report, with a link to the full document.
Influenza virus characterisation report for Europe: September to December 2013
10 Jan 2014
The latest issue of ECDC’s series on 'Influenza virus characterisation’ covers the time period since 1 September 2013.
Indicative of the late start of the 2013-14 influenza season, a low number of 46 influenza-positive specimens have been received from six EU/EEA countries so far in WHO Collaborating Centre for Reference and Research on Influenza in London.
Influenza type A viruses (91%) are dominating over type B (9%), as is often seen at the beginning of Northern Hemisphere influenza seasons. For type A, H3N2 viruses have been received in greater numbers than H1N1pdm09 viruses, with the ratio of 2:1.
The report further summarises the findings as follows:
- Compared to the 2012–13 influenza season where genetic subgroup 6C dominated among A(H1N1)pdm09 viruses, and based on the current global situation, genetic subgroup 6B viruses have been detected in increasing frequency. Subgroup 6B viruses have been antigenically similar to the vaccine virus, A/California/07/2009.
- Recently circulating A(H3N2) viruses have fallen within genetic subgroup 3C represented by the recommended vaccine virus for the 2013–14 season, A/Texas/50/2012; some new genetic clusters defined by specific HA amino acid substitutions have been observed for which antigenic characterisation is pending.
- No B/Victoria-lineage viruses have been received to date.
- Two genetic clades of B/Yamagata-lineage viruses continue to circulate: clade 3 represented by B/Wisconsin/1/2010 and clade 2 represented by B/Massachusetts/2/2012 (the recommended vaccine component for the 2013–14 influenza season). The great majority of recently circulating viruses fall within clade 2.
The report is prepared under ECDC framework contract and is based on analysis of influenza-positive specimens received by the MRC National Institute for Medical Research, the WHO Collaborating Centre for Reference and Research on Influenza in London.
