The needle - long, menacing, cold steel that delivers pain along with protection - is what people, and children in particular, hate most about vaccines.
So why can't they make the needle smaller or, better still, eliminate needles altogether like they do on Star Trek?
If you have ever asked yourself those questions, take heart, relief is on the way.
There are two new flu vaccines on the market this year that are tackling the pain problem head-on.
One, Intanza, is a shot but with a 40-gauge needle that measures only 1.5 millimetres - about the size of a mosquito proboscis and about one-10th of the size of a standard needle.
Another, FluMist, is a nasal spray.
But those technologies are barely scratching the surface for innovation and ease of delivery.
At the Canadian Immunization Conference, held recently in Quebec City, Martin Brouillette, a professor of mechanical engineering at the University of Sherbrooke, showed off a needle-free device that vaccination nurses dubbed the " Star Trek injector."
The device uses pressurized air to blast powdered vaccine through the stratum corneum (the outer layer of skin) and deeper into the epidermis.
"The advantage of this system is there is no pain, no bleeding, no bruising of the patient and no sharps that can injure the health-care worker," Dr. Brouillette said.
He said taking the needle out of vaccination can reduce the trauma for the patient and health-care provider alike, and could increase the likelihood of people opting for vaccination.
But reducing pain is not the only reason that there a real push for intradermal vaccination.
Research is showing that, done properly, injecting vaccines into the skin - as was done traditionally - is far more effective than injecting them into muscles, the most common method currently.
"With intradermal flu vaccine, 20 per cent of the regular dose is the equivalent of a full dose delivered intramuscularly," said Donna Reynolds, head of medical affairs at Sanofi Pasteur, the vaccine division of the pharmaceutical giant Sanofi-Aventis.
She said that skin is the "first line of defence" in the immune system so the antibodies in vaccines provoke a vigorous immune response. At the same time, reactions to vaccines given intradermally are lesser.
But the challenge, Dr. Reynolds said, is delivering vaccine consistently into the epidermis.
Research has showed that the outer layer of skin on adults is a pretty standard thickness of 1.5 millimetres, regardless of gender, age, race and body mass index - so Sanofi Pasteur developed a needle of that length.
The unfortunate thing, Dr. Reynolds said, is that skin thickness in children varies much more than in adults, so these products are not yet available for kids.
Precision is important: Going deeper than three millimetres means going beyond the dermis, and the vaccines become far less effective.
There are dozens of similar products under development, ranging from ultra-short needles to arrays of micro-needles.
While administering intradermal vaccines has traditionally been difficult, administering these vaccines is as easy as clicking a ballpoint pen.
In the United States, FluMist, a nasal vaccine produced by MedImmune, a division of AstraZeneca, is now commonly used to immunize children against influenza.
Raburn Mallory, clinical director of MedImmune, said the advantage of mucosal vaccines - aside from the obvious one of not requiring a needle - is that they prompt a very quick immune response. The challenge though is getting vaccine dose right.
Dr. Mallory noted that there are already a number of oral and mucosal vaccines - for cholera, rotavirus, typhoid and polio as well as the flu - but they tend to contain live virus, not killed virus such as injectable vaccines, so they can cause infection in rare instances.
The way a disease affects the body also influences the vaccination method - for example, oral vaccines are good for gastrointestinal diseases and the mucosal route is an effective way of delivering protection against respiratory illnesses.
"People wonder why we don't give all vaccines orally, and the reason is they produce the strongest immune responses in the colon and salivary glands," Dr. Mallory said.
"But we all have the same goal here, to move away from the long needle that nobody really likes."
Dr. Brouillette said the needle-free injector is near, and it can overcome some of the technical difficulties inherent with intradermal micro-needles and nasal sprays.
"The depth of the penetration is a function of particle velocity and we can adjust that to deliver the vaccine exactly where we want it in the dose we want," he said.
Dr. Brouillette and his team have developed a series of devices, including a disposable single-dose injector that costs $1 to $2 and a reusable multiple-dose injector that can deliver shots for less than 50 cents each, and they have plans for an "infinite dose" device that would cost pennies a shot.
But that's the easy part.
Currently, almost all vaccines are in liquid form. There have been compressed air injectors before, but they were plagued by problems, notably "suck back," during which vaccine was splashed and the injector was contaminated.
The new injectors deliver powdered vaccine that avoids those problems but it requires manufacturers to create powdered forms of their vaccines.
There are also concerns about the cost of the new technologies. Compared with other drugs, childhood vaccines are incredibly cheap.
Dr. Reynolds said that, realistically, new products will be more costly. "I don't know the pricing because that's not my area, but one cannot expect prices to be the same as we have now," she said.
Dr. Brouillette, on the other hand, said the only way the needle-free technology will become widely used is if it delivers cost savings.
"If these devices are going to be successful, you have to demonstrate that this approach is less costly," he said. "A little less pain is not enough."Report Typo/Error