27 January 2008
Seasonal Human Influenza Increasing in USA with persisting antiviral resistance patterns and vaccine matching for Influenza A
The current US Centers for Disease Control and Prevention (CDC) update on seasonal human influenza (A and B) for the week ending January 17th showed a slow increase in influenza activity nationwide with “widespread influenza activity” in one state (Virginia). Maryland reported “local influenza activity” and the District of Columbia reported “sporadic activity”. The full online report from the CDC can be found on their website at: www.cdc.gov/flu/weekly/
The previously noted initial pattern of antiviral resistance patterns this 2008-2009 winter flu season is persisting, as listed below:
Influenza A (H1N1): Of 103 total isolates 101/103 (98%) are resistant to oseltamivir (Tamiflu), but none (0%) are resistant to the inhaled drug zanamivir (Relenza). Both are of the newer class of anti-influenza drugs known as neuraminidase inhibitors. Only 1/103 (1%) of these H1N1 viruses was found to be resistant to the older class of antivirals known as adamantine drugs (rimantidine and amantidine).
Influenza A (H3N2) viruses: Of 23 virus isolates to date, none (0%) are resistant to either oseltamivir or zanamvir, but 23/23 (100%) are resistant to the adamantine class of antiviral drugs (i.e., rimantidine and amantidine). This pattern is the converse of that for the influenza A (H1N1) viruses as noted above.
Influenza B viruses: of 61 virus isolates to date none (0%) are resistant to oseltamivir and zanamivir. (The adamantine drugs are known not ever to be effective against influenza B viruses).
Vaccine against Influenza A (H1N1 and H3N2): Importantly, all 142 influenza A (H1) viruses that have been antigenically characterized this flu season “are related to the influenza A (H1N1) component of the 2008-2009 influenza vaccine (A/Brisbane/59/2007)”. In addition,
“all 13 influenza A (H3N2) viruses are related to the A (H3N2) vaccine component (A/Brisbane/10/2007).
Vaccine against Influenza B: “Influenza B viruses currently circulating can be divided into two distinct lineages by the B/Yamagata/16/88 and B/Victoria/02/87 viruses. Seventeen influenza B viruses tested belong to the B/Yamagata lineage and are related to the vaccine strain (B/Florida/04/2006). The remaining 35 viruses belong to the B/Victoria lineage and are not related to the vaccine strain. Thirty of the 35 viruses belonging to the B/Victoria lineage were from two states…limited to no protection may be expected when the vaccine and circulating virus strains are so different as to be from different lineages, as is seen with the two lineages of influenza B viruses.”
Thus, so far this flu season all 155 influenza A viruses that have been antigenically characterized are related to the influenza A components (H1N1 and H3N2) of this year’s flu vaccine; however, only 17/52 influenza B viruses are related to the Influenza B component of this year’s flu vaccine.
Of note, so far in this 2008-2009 flu season, 83.1% of influenza viruses have been Influenza A, and 16.9% influenza B.
The above information has stimulated discussion about the need for:
1) More specific rapid diagnostic tests for influenza that can differentiate influenza A (H1N1) from Influenza A (H3N2) from Influenza B, as well as:
2) Possibly, including two strains lineages of influenza B (e.g., as above, this year’s B/Yamagata and B/Victoria) in future human seasonal flu vaccines. If this were done, then the annual flu vaccine would contain four influenza antigens, two influenza A (H1N1 and H3N2) and two influenza B (e.g. as with this year’s circulating two strain lineages B/Yamagata and B/Victoria).
Daniel R. Lucey, MD, MPH
EROne Institutes, Department of Emergency Medicine
Washington Hospital Center
Adjunct Professor of Microbiology and Immunology
Georgetown University Medical Center, Washington, D.C.
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