Vaccinations could be made less painful by treating skin with a vaccine-laden liquid and using ultrasound to push it into the body
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.
Probably not, theres been some needleless vaccines before that did ok. If anyone has done time in the military you're probably familiar. Also any loss in efficacy could probably just be offset with higher concentrations
The smallpox vaccine was put on a sugar lump that children then ate (It really was a different time) And even after going through the digestive tract it still worked.