Supplies of the influenza vaccine could be expanded by up to five times by changing how the shot is given, administering a small dose under the skin rather than a larger dose into muscle, two teams of researchers reported Wednesday.
The new technique, which is already used for some other types of vaccines, produces just as strong an immune response as the conventional approach, studies in a relatively small number of humans have shown.
The findings probably come too late to have mucheffect on this year's flu vaccine shortage, experts said, but should provide increased flexibility in handling future outbreaks.
Using a reduced dosage could have "important public health implications," said Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases.
Dr. Myron J. Levin of the University of Colorado Health Sciences Center, chairman of the government's vaccine advisory panel, cautioned that the studies show only that recipients developed antibodies against the flu virus, not that they were protected from infection.
He said more studies would be needed before the government could officially recommend the technique.
Dr. Gregory Glenn of biotech company Iomai Corp., co-author of one of the studies, urged that the studies begin soon in case Chiron Corp. -- whose vaccine plant closure in Liverpool, England, was responsible for the current shortage -- is unable to produce vaccine next year as well.
"We could, if we get going soon, expand this to enough people that we could recommend the approach with confidence for next year," he said.
Iomai, located in Gaithersburg, Md., is developing new ways to administer vaccines under the skin. Because the skin is normally in contact with the hostile world of germs, he said, it has a much more competent immune system than the muscles where vaccines are traditionally administered. As a result, smaller doses can be used.
The second study was conducted by Dr. Robert B. Belshe and his colleagues at Saint Louis University and the University of Rochester. The two papers, plus an editorial by Fauci and Dr. John R. La Montagne of the National Institute of Allergies and Infectious Diseases, are scheduled for publication in the Nov. 25 issue of the New England Journal of Medicine, but were published online Wednesday because of the current flu vaccine shortage.
Although the two groups used slightly different protocols, each administered a flu vaccine to about 100 people using the conventional technique and to another 100 people under the skin. Belshe's group used 40 percent of the normal dose; Glenn's used 20 percent. Both found that the level of antibodies produced by vaccination under the skin was comparable to that produced by the normal vaccination.
Some physicians have long used the technique. Dr. Warren Warwick of the University of Minnesota said he has been using the approach for nearly 40 years for family, friends and selected patients who refuse intramuscular injections because they develop severe reactions to them. None of them has ever caught the flu, he said.
Intradermal vaccination is commonly used in other countries to administer the tuberculosis vaccine and the rabies vaccine.
The technique uses a small, readily available syringe. It takes about a minute to give the shot, compared to a few seconds for the conventional jab. If injected too far below the skin, the vaccine is not effective.
"But this is not rocket science," Belshe said. "Most doctors and nurses are trained to do it" because of tuberculosis testing, which uses a similar method.
The biggest drawback to the technique is that it does not appear to be as effective for the elderly, who have weakened immune systems. But Iomai has developed a Band-Aid-like patch for the arm containing an immunostimulant that enhances the activity of the vaccine.