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Findings in New England
Journal of Medicine point to younger populations
TEMPE, Ariz. – There is no
way to know how the newest strain of the H1N1
influenza virus will behave in the future. But
scientists, notably those working at the
intersections of epidemiology, mathematics,
modeling and statistics, are monitoring it
closely to identify anomalies on its pattern of
spread while evaluating ways of mitigating its
impact.
"Public health officials
have the ability to track confirmed cases and
hospitalizations in real-time with modern data
collection approaches and the aid of modeling as
well as the ability to quickly identify new
strains and track their evolution," says
mathematical epidemiologist Gerardo Chowell-Puente,
an assistant professor at Arizona State
University's School of Human Evolution and
Social Change in the College of Liberal Arts and
Sciences.
Chowell-Puente is co-author
of a new study of the A(H1N1) influenza pandemic
strain circulating around the world. The study's
findings reveal an age shift in the proportion
of cases toward a younger population when
compared with historical patterns of seasonal
influenza in Mexico. The findings are published
June 29 online in the New England Journal of
Medicine. Other authors of "Reported severe
respiratory disease and deaths concurrent with
atypical A(H1N1) influenza circulation of swine
origin in Mexico, 2009" include Stefano Bertozzi
and Arantxa Colchero, Mexico's National
Institute of Public Health; Hugo Lopez-Gatell,
Celia Alpuche and Mauricio Hernandez, Mexico
Ministry of Health; and Mark A. Miller, National
Institutes of Health Fogarty International
Center,
"The data show that the
vast majority of cases of severe pneumonia and
deaths occurred among those ages between 5 and
59, which is atypical when compared with the age
pattern supported by seasonal flu," says Chowell-Puente.
"If resources or vaccine supplies are limited,
focusing prevention efforts on these age classes
must be considered."
Specifically, according to
the findings, 87 percent of the deaths and 71
percent of the cases of severe pneumonia
occurred in persons aged 5-59, compared to an
average 17 percent and 32 percent, respectively,
for influenza seasons from 2006 through 2008.
"These findings suggest relative protection for
those persons exposed to H1N1 influenza viruses
during childhood prior to the 1957 pandemic,"
Chowell-Puente says.
Chowell-Puente and other
mathematicians and biostaticians attending a
swine flu workshop at Arizona State University
June 25-28, note that vaccines and anti-viral
medications are in limited supply.
"Because achieving high
vaccination rates before the fall is not
feasible with current technologies, effective
distribution of a limited vaccine and antiviral
stockpiles will be crucial to mitigate a
potential second pandemic wave. The seasonal
influenza vaccination strategy focuses on the
very young and the very old – the most
vulnerable populations. This is not necessarily
the case for pandemics as we showed in our
study."
According to Chowell-Puente,
the key to containing pandemic flu is closely
tied in to the ability to quickly produce a good
stockpile of vaccines and following a reactive
distribution plan that targets the appropriate
age cohorts of the population. The first wave of
the current strain has not been particularly
deadly, but subsequent waves may be more
virulent, though it is too early to tell, he
notes.
"For the 1918 ("Spanish
flu") influenza pandemic, this was the pattern –
first a mild wave, and then a severe one with
higher case fatality rates," notes
Chowell-Puente.
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