Flu Vaccine's Skin Injection Might Stretch Supply
By DENISE GRADY
Published: November 4, 2004
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It may be possible to stretch the supply of flu vaccine by giving some
people reduced doses that are injected into the skin instead of the
usual site, a muscle, researchers are reporting.
Two research teams tested the idea - using 40 percent of the normal dose
in one study, 20 percent in the other - and found that in healthy adults
up to age 60, smaller doses in the skin worked just as well as
full-sized ones shot into muscle. But in people older than 60, the
technique, called an intradermal injection, was less successful. They
probably need larger doses, researchers found.
The two studies, to be published on Nov. 25 in The New England Journal
of Medicine, have been posted on the journal's Web site,
www.nejm.org , ahead
of time because of "potential public health implications," the editors
Though the findings may sound like a solution to the current vaccine
shortage, researchers said they would actually be of limited use.
"I think it would be premature to start using an intradermal approach,"
said Dr. Mitchell L. Cohen, an infectious disease expert at the federal
Centers for Disease Control and Prevention. "The studies are very
promising but need to be repeated in larger populations."
Combined, the studies included only 338 people. And researchers used
blood tests, not cases of influenza, to measure how the immune system
responded to the vaccine.
Dr. Anthony S. Fauci, head of the National Institute of Allergy and
Infectious Diseases, said, "Is this going to bail us out this year?
Dr. Fauci, who wrote an editorial accompanying the two studies, said low
doses were most likely to be least effective in some of the people who
need vaccine most: the elderly and those with H.I.V. or chronic diseases
that affect the immune system.
But he also said that low doses would probably work in others who should
be vaccinated, like people who have asthma but are otherwise well, and
healthy people who take care of infants or high-risk patients.
"There is no doubt in my mind that physicians who are frustrated that
they have very few doses are going to read these papers and take it upon
themselves" to split vaccine doses among their patients, Dr. Fauci said.
"There will be physicians who will make that judgment call," he said. "
'I have 200 patients and 75 doses, I have to do something about that.' "
Even though flu vaccine is approved only for intramuscular injections at
full strength, it would not be illegal for doctors to split doses and
inject them under the skin, because once a drug is on the market,
doctors can use it in ways and for conditions for which it was not
approved or labeled. Such "off-label" use is common with many drugs, and
Dr. Fauci said he would be "astounded" if any regulator tried to
interfere with doctors who tried to stretch their vaccine supplies by
The advantage of injecting the vaccine into the skin is that the skin
has a rich supply of dendritic cells, a type of white blood cell that
can initiate a powerful immune response.
"The skin is an important immunological organ, and if we inject flu
vaccine into the skin you can get a really good immune response with a
very small amount of vaccine," said Dr. Robert B. Belshe, director of
the center for vaccine development at Saint Louis University and the
leader of one of the studies.
The other study was conducted by researchers at the Iomai Corporation in
Gaithersburg, Md., a company that specializes in delivering vaccines to
Dr. Fauci said the intradermal technique was so promising that it should
be studied further and might ultimately prove to be the best way to
provoke a vigorous immune response in chronically ill people, whose
immune systems sometimes fail to react strongly enough to derive
protection from vaccines.
Doctors may need lessons in how to give intradermal shots. The technique
is the same one used to inject substances into the skin to test for
"It takes a little bit of training, but we teach medical students to do
it in 15 minutes," Dr. Belshe said.
Intradermal shots are given with a shorter, finer needle than are
intramuscular shots. The needle is inserted between the layers of the
skin, and when the vaccine is injected it forms a blisterlike bubble.
"You can see it, and you know when you've done it right," Dr. Belshe
The injection itself hurts less than an intramuscular shot, but the site
of the intradermal shot gets redder, a sign of the robust immune
response, he said, adding that the redness is trivial.
Dr. Belshe said researchers should do the studies needed to get approval
from the Food and Drug Administration for low-dose, intradermal flu
shots for some patients.
"We are in an era of increasing need for influenza vaccine," he said,
"so this is an area that we need to pursue quickly."