Fictional worlds can make up their own rules. But everything needs to be governed by CONSISTENT rules, whether it's physics, biology, astronomy, etc. For example, if you want an alien species without lips to speak perfect English. you must explain how it is possible, given the fact that many words in the English language are articulated using bilabial or labiodental consonants. Same for magic, which needs different laws of physics, as most magic spells violate the Law of Conservation of Mass.
It has been established in previous Sims games (Ambitions, Get to Work) that vaccines are administered through the subcutaneous route with a needle or special device. Any explanation they could give now will CONTRADICT what has been previously established (canon).
At the end of the day, it's just a bunch of excuses apologists or developers make up for lazy animations. It's ridiculous to pretend there's some deep lore behind throwing vaccines like drinks when it's pretty clear it was the result of laziness.
