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.
Website for this posting (requires
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