The dictionary definition of "need" is instructive. The first definition (in Collins 2018) is "to be in want of", so in a sense you're right. However, one of

The dictionary definition of "need" is instructive. The first definition (in Collins 2018) is "to be in want of", so in a sense you're right. However, one of the subsequent definitions is "distress or extremity", followed by "extreme poverty or destitution". "Need", then, is a want that's extreme enough to cause suffering if it's unfulfilled. In that sense, people did need antibiotics. They might not have known it, but they did. In the same way, today we need treatments that we haven't discovered yet. "Being able to survive" isn't the bar. "Not suffering for the lack" is.