You overestimate the intelligence of Sinkees. When the world calls it a vaccine, they will forever call it a vaccine.
A term like Immunotherapy will get you nowhere because they cannot wrap their small brains around big-sounding words. The gahment understands the psyche of Sinkees and that is why we have the largest number of acronyms to describe all things SG - CPF, PIE, SAF, HDB, POSB, MOM, MOE, MOH,... the list goes on.
I bet the majority od sinkees don't even know what CPF stands for but they know what it is.