Injections are an important and inevitable lynchpin of modern medicinal techniques. The idea is to force liquid directly into the body using a hollow needle to penetrate the skin. Without these kinds of jabs, the medical landscape would be inestimably poorer.
But injections have a number of downsides. They are an important source of disease transmission, particularly when needles are re-used and in the event of needle-stick injuries to health professional, they are painful and the needles are difficult and dangerous to dispose of. Then there's needle phobia and so on.