You're probably correct. The trouble is that it's so much easier to put a couple of live vaccine drops on the tongue than to vaccinate by needle. No matter how

You're probably correct. The trouble is that it's so much easier to put a couple of live vaccine drops on the tongue than to vaccinate by needle. No matter how painless modern injections are people still don't like having them thus the deterrence rate is higher. It's a key factor if we're trying vaccinate the whole population.