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Injecting flu vaccine into the skin instead of muscle could stretch limited supplies, two studies reported Wednesday.
Researchers injected less than half the standard flu vaccine dose into the skin. Yet, in young to middle-aged healthy people, they were able to generate roughly the same immune response as conventional flu shots, which are injected into muscle.
There has been increasing interest in delivering vaccines into the skin. The reason: As the body's first line of defense, the skin is loaded with cells on guard against foreign microbes. When they encounter such microbes, these cellular sentries launch an immune response to deter them.
Authors of the new studies say government health experts are greatly interested in their findings, but it's not clear what effect they might have on this season's flu vaccine shortage.
The Food and Drug Administration has not approved in-the-skin administration of flu vaccine, although doctors and nurses are free to try this ''off-label'' use, says Robert Belshe, lead author of one of the new studies, which were posted on The New England Journal of Medicine's Web site.
Injecting vaccine into the skin is trickier than injecting it into muscle, but it's easy to learn and can be done with the same needles used for the tuberculosis skin test, says Belshe, director of vaccine development at Saint Louis University.
His team randomly assigned 238 healthy volunteers 18 and older to get flu shots either in the skin or in the muscle. The shots in the skin contained 40% as much vaccine as the standard shots. In participants 18 to 60, the immune response to the two flu shots -- as measured by antibody levels in the blood -- didn't differ significantly. Although older volunteers in both groups also had a vigorous antibody response, the standard flu-shot group tended to have a greater response.
''The million-dollar question is, how much antibody do you need to be protected from flu?'' Belshe says.
Immune response to the flu vaccine begins declining at around age 35, says Gregory Glenn, co-author of the second study and chief scientific officer at Iomai, a company in Gaithersburg, Md. Iomai is testing a small patch, placed over the flu shot site, to boost the immune response to the standard flu shot.
As part of their research, the Iomai scientists randomly assigned 100 healthy volunteers ages 18 to 40 to either the standard flu shot or an in-the-skin shot using just a fifth as much vaccine. They found that the immune response to one of the vaccine's three flu virus strains was superior in the group getting shots in the skin. The two groups had comparable responses to the other two strains.
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