"This is not new," said flu expert Dr. Marc Siegel, an associate professor of medicine at the New York University School of Medicine.
"Basically, these studies emphasize a point we have known for a while, which is that H1N1 is particularly problematic for the young and for pregnant women," Siegel said.
The reason that the H1N1 flu hits these groups the hardest is that they don't have immunity from exposure to other similar viruses, Siegel explained.
"With pregnancy there is an additional problem, since these women are immunocompromised to some extent," he added.
Siegel also said these findings are in keeping with past pandemics. "The young are more at risk even in non-flu season, because there is no prior immunity to any flu," he pointed out.
Seasonal flu does confer some immunity, Siegel added. "Over time, immunity to the H1N1 flu will build up and it will become a seasonal flu strain," he said.
Another study, this one in ferrets, reinforces that point. Published in the Dec. 23 issue of Science Translational Medicine, researchers found that animals exposed to seasonal flu vaccine had more immunity to the H1N1 flu than ferrets never vaccinated against the seasonal flu.
The researchers discovered that a higher concentration of antibodies against seasonal flu in the ferrets increased protection from H1N1 infection.
Why the seasonal flu vaccine, although not able to protect against H1N1 virus, enhances the immune response isn't known, as is whether or not this effect works in humans.
For more information on H1N1 flu, visit Flu.gov.
SOURCES: Ken August, spokesman, California Department of Public Health, Sacramento, Calif.; Marc Siegel, M.D., associate professor, medicine, New York Un
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