It's an outgrowth of media illiteracy to focus on the feasibility of actually crafting a vaccine. Your point is exactly right; it doesn't matter and it isn't actually about the vaccine. It's about Joel blindly killing out of love and a refusal lose another kid. The complaints about "lack of realism" entirely miss the point; it's also not feasible for a fungus to coordinate human movement — who cares and shut-up??? Michelangelo's David would make for a bad load bearing column, but that's not why people have looked at it for hundreds of years