Seasonal Flu Shot Some Help vs. Swine Flu?
Mexican Study: Some H1N1Swine Flu Protection in Seasonal Shot; U.S. Data Show No Support for This Conclusion
Daniel J. DeNoon
WebMD Health News
Louise Chang, MD
Oct. 6, 2009 -- A small study of Mexican H1N1 swine flu patients suggests
that seasonal flu shots might offer some protection against the new flu. But
CDC data show no hint of such protection.
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The study, which looked at patients of a small respiratory disease hospital
in Mexico City, showed that those who received a flu vaccine during the
2008-2009 flu season were 73% less likely to have been infected with H1N1 swine
flu than unvaccinated patients.
Moreover, the study suggested that seasonal flu vaccine might make H1N1
swine flu less severe. There were no deaths among the eight vaccinated patients
who came to the hospital with lab-confirmed H1N1 swine flu. But among 52
unvaccinated patients with H1N1 swine flu, 18 died.
Despite the findings, which they call "preliminary," study researchers
Lourdes Garcia-Garcia, MD, of Mexico's National Institute of Public Health, and
colleagues, warn that seasonal flu vaccination is not sufficient protection
against H1N1 swine flu.
"Notwithstanding this contribution to protection, a specific vaccine against
A/H1N1 2009 [swine flu] is crucial," they conclude in their report, published
in the advance online issue of BMJ.
The Mexican data stand in stark contrast to U.S. data and Australian data,
which show no hint that seasonal flu vaccination has any effect on the current
H1N1 swine flu.
An unpublished study from Canada reportedly showed just the opposite of the
Mexican study -- that seasonal flu vaccine might make people more vulnerable to
H1N1 swine flu. U.S. and Australian data offer no support for this hypothesis,
It's "biologically conceivable" that seasonal flu vaccine might offer some
protection against H1N1 swine flu, says flu expert John Treanor, MD, chief of
infectious diseases at the University of Rochester, N.Y.
"We would not predict the protection would be very robust," Treanor tells
WebMD. "This does not suggest in any way that we don't need a vaccine for H1N1
There are CDC data suggesting that older people -- possibly due to exposure
to a seasonal H1N1 virus that circulated before 1957 -- may have some slight
protection against H1N1 swine flu.
And the fact that adults become protected against H1N1 swine flu after just
a single dose of the new H1N1 swine flu vaccine suggests some kind of priming,
either exposure to or vaccination against seasonal H1N1 virus.
Treanor suggests that this is because the current flu pandemic is something
different than scientists have ever before seen. It's certainly not like a
seasonal flu, but it's also not quite like the more severe flu pandemic that
had been feared.
"We are learning it is possible to have something between a full blown
pandemic and just a bad season," Treanor says. "You see this high
transmissibility with relatively low mortality. It's not what you might see
with a totally new [human flu virus] and it's not what you see in a bad flu
SOURCES: Garcia-Garcia, L. BMJ, Online First edition, Oct. 7, 2009.
De Jong, M. and Sanders, R.W. BMJ, Online First edition, Oct. 7, 2009.
John Treanor, MD, chief of infectious diseases; professor of medicine; professor of microbiology and immunology, University of Rochester, N.Y.
Tom Skinner, senior public information officer, CDC.
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