ST. LOUIS — There might be a way to get a flu shot without a shot. St. Louis University researchers are getting flu vaccine under the skin of volunteers without needles.
The SonoPrep, an ultrasound device made by Sontra Medical Inc., opens skin pores so that vaccine can seep through. Nothing ever touches nervy muscles.
‘‘There's a machine and there's a sensation. But if there's no needle, that takes away the biggest fear,'' said Dr. Robert Belshe, director of the Center for Vaccine Development at St. Louis University.
At least 10 percent of the adult population has a severe fear of needles, according to a 1995 study in the Journal of Family Practice. Belshe hopes the new method will encourage the phobic to get in for their needleless flu shots.
The method is not only pain-free but also uses less vaccine, according to research Belshe published in November in the New England Journal of Medicine. Belshe found that less than half of the normal muscular dose worked just as well when injected into the skin only.
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Belshe said researchers have for decades known about the skin's superior ability to create antibodies in response to a vaccine. It makes sense, he said, since the skin needs plenty of immune defenses to deal with cuts and scrapes.
‘‘But there wasn't any reason to look at it until we had a vaccine shortage,'' he said.
The trial used the tiny skin-pricking needles of tuberculosis syringes and found that 40 percent of the normal dose was just as effective for 18- to 60-year-olds, and nearly as effective for older people.
Franklin, Mass.-based Sontra contacted Belshe after reading the paper, hoping to try it without any needles at all. In August, the company won FDA approval for SonoPrep, which was originally used to deliver a skin-numbing drug. Sontra also has tested it as a way to deliver insulin, and is currently conducting a hepatitis vaccine trial in Worcester, Mass.
The St. Louis flu vaccine trial, which began in April, will test 60 volunteers between the ages of 18 and 49.
Nurse Jan Tennant said that, so far, only a few people have complained of a tingling sensation created by the hand-held device.
Inside the SonoPrep is a vibrating horn. The vibrations make thousands of microscopic bubbles in a thin layer of soap water on the skin, said Shikha Barman, a Sontra researcher.
The outermost layer of skin is made up of hardened dead cells held together by fats, like bricks and mortar. The bubbles open pores and create pathways by dissolving the fatty ‘‘mortar.''
The bubbles also disrupt the natural electrical conductivity of skin, Barman said. The SonoPrep shuts off once it detects the conductivity for a certain pore size.
Other things, like water, can change the permeability of skin. But the SonoPrep does it in seconds and to the same level, regardless of your skin's oiliness, Barman said.
‘‘If you could simply take a shower and slap on a vaccine patch, that product would be out there,'' she said.
Nurses next place a doughnut-shaped patch on the skin, within which goes a drop of vaccine. The vaccine seeps through the epidermis to dendritic cells, immunilogic sentinels that eat the vaccine and ‘‘show'' it to the immune system in nearby capillaries, which produce antibodies. Nothing reaches nerve cells in the deeper dermis.
In a month, Belshe will see how many antibodies the volunteers produced in response to the vaccine. He said it would likely be two years before the method could be approved for routine use.
Barman said SonoPreps cost about $2,000.
