Influenza Vaccine a Good Match for Circulating Strains

We are seeing a quick rise in the number of influenza cases in the office. We are identifying both influenza A and B with our rapid tests. While we have had a few patients test positive for influenza even though they received this year’s vaccine, the data from the CDC is so far showing a good match between the strains contained in the vaccine and the strains that are causing illness. The strains are also sensitive to oseltamivir (Tamiflu) so far this season.

Here is an excerpt from the CDC’s Influenza Update:

Antigenic Characterization:
CDC has antigenically characterized 89 influenza viruses [13 2009 influenza A (H1N1) viruses, 26 influenza A (H3N2) viruses, and 50 influenza B viruses] collected by U.S. laboratories since October 1, 2010.

2009 Influenza A (H1N1) [13]

All 13 were characterized as A/California/7/2009-like, the influenza A (H1N1) component of the 2010-11 influenza vaccine for the Northern Hemisphere.
Influenza A (H3N2) [26]

All 26 were characterized as A/Perth/16/2009-like, the influenza A (H3N2) component of the 2010-11 influenza vaccine for the Northern Hemisphere.
Influenza B [50]

All 50 viruses belong to the B/Victoria lineage of viruses and was characterized as B/Brisbane/60/2008-like, the recommended influenza B component for the 2010-11 Northern Hemisphere influenza vaccine.
Antiviral Resistance:
Testing of 2009 influenza A (H1N1), influenza A (H3N2), and influenza B virus isolates for resistance to neuraminidase inhibitors (oseltamivir and zanamivir) is performed at CDC using a functional assay. Additional 2009 influenza A (H1N1) clinical samples are tested for a single known mutation in the neuraminidase protein of the virus that confers oseltamivir resistance (H275Y). The data summarized below combine the results of both test methods and includes samples that were tested as part of routine surveillance purposes; it does not include diagnostic testing specifically done because of clinical suspicion of antiviral resistance.

High levels of resistance to the adamantanes (amantadine and rimantadine) persist among 2009 influenza A (H1N1) and A (H3N2) viruses (the adamantanes are not effective against influenza B viruses) circulating globally. As a result of the sustained high levels of resistance, data from adamantane resistance testing are not presented weekly in the table below.

To prevent the spread of antiviral resistant virus strains, CDC reminds clinicians and the public of the need to continue hand and cough hygiene measures for the duration of any symptoms of influenza, even while taking antiviral medications. Additional information on antiviral recommendations for treatment and chemoprophylaxis of influenza virus infection is available at http://www.cdc.gov/flu/antivirals/index.htm.

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