They were both known early on thanks to the outbreak on the Diamond Princess, which was a perfectly sealed environment yielding data on the worst case scenario

They were both known early on thanks to the outbreak on the Diamond Princess, which was a perfectly sealed environment yielding data on the worst case scenario (cruise ships are full of the elderly). Officials just ignored it. But it was also known that IFRs measured early on in an epidemic are always too high, because the less serious cases don't get reported or detected. There's discussion of that problem in the literature pre-dating COVID. So you'd expect some attempt to compensate for that, which there wasn't. And finally once more accurate data did become available, epidemiologists typically ignored it. They were still happily publishing models assuming a 1% IFR in 2021. W.R.T. acting in the face of unknowns, no, would not agree. The precautionary principle can be used to justify literally any action no matter how crazy. It's informally called the politician's fallacy (something must be done, this is something, therefore it must be done). You do have to make decisions based on data. Not having data or understanding doesn't give permission to make everyone do literally anything you want. It means you can't take morally legitimate action until you do have that understanding.