Vaccines can be delivered through the skin using ultrasound. This method doesn’t damage the skin and eliminates the need for painful needles. To create a needle-free vaccine, Darcy Dunn-Lawless at the University of Oxford and his colleagues mixed vaccine molecules with tiny, cup-shaped proteins. They then applied liquid mixture to the skin of mice and exposed it to ultrasound – like that used for sonograms – for about a minute and a half.
My favorite anecdote, though not necessarily mine, about jet inoculation comes from the army. They had long lines of men to immunize and little time to do it. Walk up, hold still, hear the click, feel the water pierce you, walk away sore. However, if anyone moved even slightly during the process, the needle of water becomes a knife, slicing their shoulder open. It was not a well thought out mechanism.