Seasonal Influenza Activity Increasing Across Europe - H3N2 Dominant Strain

Latest surveillance data coming through the European Centre for Disease Prevention and Control (ECDC) from virologists and clinicians indicates that the influenza A(H3N2) virus is the predominant strain in Europe so far this season. Based on the data published by ECDC Roche confirms that the oral antiviral Tamiflu (oseltamivir) is fully active against influenza A(H3N2) and influenza B, which currently comprise 94 percent of circulating viruses in Europe this year.(1)


Tamiflu resistance reported in the 2008-2009 influenza seasons is confined to H1N1. No resistance has been seen with other circulating seasonal viruses - H3N2 and influenza B.


"Recent media reporting has elevated awareness of the H1N1 seasonal resistance seen this year in the United States and the Far East. However, in Europe the picture is different with H3N2 being the dominant strain so far. The circulating H3N2 viruses, which often cause a more severe illness than H1N1, are sensitive to oseltamivir, which means that oseltamivir will be active against the vast majority of influenza infections in Europe this season, if current trends continue," comments Prof Albert Osterhaus, Head of Virology, Erasmus Medical Centre, Rotterdam. "It is important that doctors understand that oseltamivir remains an effective treatment for patients across Europe."


Vaccines are considered first line in the management of seasonal influenza, however, people who show symptoms or have been in close contact with an infected person may require more immediate intervention, such as Tamiflu, which can rapidly treat and prevent influenza.


European surveillance data


The ECDC reports that in the 2008-2009 season, influenza activity is increasing rapidly across Europe. The first countries to report high intensity of influenza activity were Portugal and Ireland. To date, medium or high intensity activity has been reported in nineteen countries.(1) Of 2488 viruses which have been typed and sub-typed in Europe so far this influenza season, the majority, 2128, were H3N2, with a smaller proportion,141, subtype H1N1 and 219 were type B. The data to date indicate that influenza A (H3N2) and B viruses which Tamiflu is active against make up over 90 percent of the viruses circulating in Europe based on the latest information.(1)


US surveillance data


While influenza A(H1N1) has been the most common strain circulating in the US so far this season, the Centers for Disease Control and Prevention (CDC) has noted that it is early in the flu season and it is difficult to predict this season's dominant strain. Last season in the US, the dominant influenza strain changed from H1N1 to H3N2 in late January.















In December 2008, the CDC issued interim guidance for the 2008-2009 influenza season which recommends treatment with either zanamavir or Tamiflu in combination with rimantadine when influenza A(H1N1) virus infection or exposure is suspected.(2) The CDC has reminded clinicians to remain alert for additional changes in recommendations as the influenza season progresses.


At the same time ECDC noted that the epidemiological situation was different in Europe and that therefore the same considerations might not apply in Europe. Infections with influenza A(H3N2), the predominant strain in Europe this season, or B viruses can be treated with either Tamiflu or zanamavir.


In addition to monitoring by government agencies, WHO collaborating laboratories and other public health institutions, Roche recently initiated the global Influenza Resistance Information Study (IRIS), which will include 1,200 patients per influenza season from 2008-2011. Roche also continues to support the activities of the Neuraminidase Inhibitor Susceptibility Network (NISN).


Sensitivity of H5N1 (bird flu) to Tamiflu


Recently published data confirms that the H5N1 avian influenza (bird flu) strain remains sensitive to Tamiflu. Greater than ninety nine percent of H5N1 samples studied did not exhibit mutations that confer oseltamivir resistance.(3)


According to Benjamin Schwartz, MD, CDC National Vaccine Program Office, "the mutations that have made the H1N1 virus resistant are unlikely to occur in a pandemic virus, so therefore we have not changed our recommendations for planning and stockpiling".(4) Tamiflu remains the World Health Organization's "primary recommended antiviral agent of choice for the treatment of A(H5N1) virus infections".(5)


References


(1) EISS - Weekly Electronic Bulletin Week 2 :05/01/2009-11/01/2009 16 January 2009, Issue No 287


(2) The Centres for Disease Control and Prevention (CDC). Interim Antiviral Guidance for 2008-09 www2a.cdc/HAN/ArchiveSys/ViewMsgV.asp?AlertNum=00279 Accessed 6 January 2009


(3) Hill AW et al. Evolution of drug resistance in multiple distinct lineages of H5N1 avian influenza. Infections, Genetics and Evolution. 2008


(4) 'Cost, resistance aired in HHS webcast on antivirals'.


(5) Clinical management of human infection with avian influenza A(H5N1) virus.


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