SEASONAL INFLUENZA (H3N2) VIRUS - POTENTIAL VACCINE MISMATCH
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A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
Date: Thu 23 Jul 2009
Source: The Edmonton Sun, The Canadian Press report [edited]
More flu vaccine woes
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Another storm may be brewing for the coming flu season: A component
of the seasonal flu shot may not be well matched to the circulating
viruses, potentially setting up what's known as a vaccine mismatch.
Some samples of the emerging new strain of H3N2 viruses show a
substantially reduced response to antibodies generated by the
corresponding virus in the seasonal vaccine, raising the possibility
of significantly reduced protection in some cases.
Vaccine mismatches are bad at the best of times. More people get sick
during flu seasons with mismatches. But a seasonal flu vaccine
mismatch coinciding with a flu pandemic? That is no one's idea of a
good time. Dr. Allison McGeer groaned when she heard a new H3N2
variant is circulating in some parts of the Southern Hemisphere.
"It's going to be a long winter. I know that already," said McGeer,
an influenza expert and head of infection control at Toronto's Mount
Sinai Hospital. "It's not going to be pleasant because ... it's going
to be one big long influenza season, from some time in September
until next May."
The new variant has been seen on a number of continents, though it
still remains a minority member of the H3N2 [strains], according to
experts at the World Health Organization (WHO) and the U.S. Centers
for Disease Control and Prevention (CDC) in Atlanta. With the demands
the ongoing pandemic is placing on the WHO's laboratory network,
researchers haven't yet had time to study whether the new variant is
making up a growing percentage of H3N2 viruses, said Dr. Nancy Cox,
director of the CDC's influenza division. If they were, that would
suggest the variant was on its way to becoming the dominant H3N2
virus and a vaccine mismatch would be on the cards.
Further clouding the issue is the fact that labs around the world
haven't been submitting as many H3N2 viruses to the WHO network.
There are simply fewer of them around. "We haven't had that many H3N2
viruses to analyze because we've had such a flood of the novel H1N1
viruses because they're predominating," Cox said. Dr. Wenqing Zhang
of the WHO's global influenza program said many Southern Hemisphere
countries are just coming into their regular flu seasons. The next
month or so will give the world a clearer picture as to whether the
pandemic virus will crowd out the previous influenza A subtypes --
making the composition of the seasonal vaccine less relevant -- or
whether one or both of the seasonal flu A virus [subtypes] will
continue to circulate. And if H3N2 sticks around, the coming weeks
will also offer a sign as to whether this new variant is likely to
complicate the upcoming Northern Hemisphere flu season.
"While seemingly this variant H3 is emerging, we do not know to what
extent it will be circulating," Zhang said by e-mail from Geneva. Cox
said the WHO collaborating labs will be heightening surveillance for
seasonal flu viruses in the lead-up to the WHO's strain selection
meeting for the Southern Hemisphere seasonal vaccine, held in
September [2009]. One place they'll be checking is virus samples from
nursing homes. H3N2 viruses prey on seniors and are behind many of
the frequent flu outbreaks seen in long-term care facilities. For
some reason, nursing home outbreaks are rarely caused by seasonal
H1N1 viruses and so far the influenza pandemic (H1N1) 2009 virus has
largely spared that population too. "If we start to see outbreaks in
those types of settings, this would increase our level of concern,"
Cox said. "We haven't seen that to date."
Because it takes months to make and ship flu vaccine, the viruses
covered by the seasonal flu shot have to be chosen long in advance.
For the Northern Hemisphere vaccine, experts like Cox gather at the
WHO in February [2009] to assess the viruses circulating and make
their best estimates of which will be the major disease sources in
the following winter. For the 2009-2010 winter they chose an H3N2
virus called A/Brisbane/10 first spotted in 2007. But within weeks of
the decision hints emerged that there was a new H3N2 variant, one
sufficiently mutated ("drifted" in the language of flu) that it might
be able to evade the vaccine.
Researchers in the influenza lab at the British Columbia Centre for
Disease Control spotted it in early March [2009] as they were
conducting late-season surveillance looking for just such viral
evolution. In early May [2009], they reported the finding on
ProMed-mail, an electronic bulletin board and mailing list which
monitor infectious diseases outbreaks around the world [Influenza A
(H1N1) - worldwide (11): coincident H3N2 variation 20090505.1679].
Dr. Danuta Skowronski, an influenza expert at the BCCDC, said she is
expecting this new variant to take over as the dominant H3N2 strain.
And since the swine flu virus isn't infecting older adults much, it
could leave a niche for the new H3 variant. "So it's hard to know. We
just have to prepare for that possibility either way," Skowronski
said. "The idea of having a mismatched drift strain circulating the
same year that we also have swine influenza [influenza pandemic
(H1N1) 2009 virus infection] may mean that all segments of the
population are affected by influenza one way or the other, whether
it's the elderly with H3N2 and the young with H1N1."
[Byline: Helen Branswell]
--
Communicated by:
ProMED-mail Rapporteur Mary Marshall
[For an up-to-date detailed account of the prevention and control of
seasonal influenza with vaccines, readers should consult the recently
published "Recommendations of the Advisory Committee on Immunization
Practices (ACIP), 2009." MMWR Early Release Fri 24 July 2009 / 58
(Early Release document);1-52, available at:
"This report updates the 2008 recommendations by CDC's Advisory
Committee on Immunization Practices (ACIP) regarding the use of
influenza vaccine for the prevention and control of seasonal
influenza (CDC. Prevention and control of influenza: recommendations
of the Advisory Committee on Immunization Practices [ACIP]. MMWR
2008;57[No. RR-7]). Information on vaccination issues related to the
recently identified novel influenza A H1N1 virus will be published
later in 2009. The 2009 seasonal influenza recommendations include
new and updated information. Highlights of the 2009 recommendations
include 1) a recommendation that annual vaccination be administered
to all children aged 6 months--18 years for the 2009-2010 influenza
season; 2) a recommendation that vaccines containing the 2009-2010
trivalent vaccine virus strains A/Brisbane/59/2007 (H1N1)-like,
A/Brisbane/ 10/2007 (H3N2)-like, and B/Brisbane/60/2008-like antigens
be used; and 3) a notice that recommendations for influenza diagnosis
and antiviral use will be published before the start of the 2009-2010
influenza season. Vaccination efforts should begin as soon as vaccine
is available and continue through the influenza season. Approximately
83 percent of the United States population is specifically
recommended for annual vaccination against seasonal influenza;
however, <40 percent of the U.S. population received the 2008-2009
influenza vaccine.
These recommendations also include a summary of safety data for U.S.
licensed influenza vaccines. These recommendations and other
information are available at CDC's influenza website
(http://www.cdc.gov/flu ); any updates or supplements that might be
required during the 2009-2010 influenza season also can be found at
this website. Vaccination and health-care providers should be alert
to announcements of recommendation updates and should check the CDC
influenza website periodically for additional information."
The 2009 recommendations include 3 principal changes or updates, one
of which is that: The 2009-2010 trivalent vaccine virus strains are
A/ Brisbane/59/2007 (H1N1)-like, A/Brisbane/10/2007 (H3N2)-like, and
B/ Brisbane 60/2008-like antigens. - Mod.CP]
[see also:
Influenza A (H1N1) - worldwide (11): coincident H3N2 variation 20090505.1679]
....................cp/ejp/lm
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