Researchers are investigating the potential of a painless, needle-free vaccine delivery by ultrasound. The method uses cavitation, which is the formation and popping of bubbles in response to a sound wave. Though initial in vivo tests reported 700 times fewer vaccine molecules were delivered by the cavitation approach compared to conventional injection, the cavitation approach produced a higher immune response. The researchers theorize this could be due to the immune-rich skin the ultrasonic delivery targets. The result is a more efficient vaccine that could help reduce costs and increase efficacy.