There are degrees of uncertainty, and ranges of plausible severity, even when we haven't actually nailed these down quantitatively. We already have enough information about COVID-19 to raise it far above the threat level of a random virus. And given how quickly and stealthily it seems to be capable of spreading, to take no action beyond 'pursuing more information' would be almost the same as assuming the best possible resolution of our uncertainty. That's no more rational than the other extreme of assuming the very worst.

I am. The most important factor here is Ro not uncertainty. Maybe I should emphasize it more.

I was replying specifically to when you said "Also this is a novel virus which means this strain is new and may be unpredictable. Mutations may occur." I interpreted that as meaning that because of our lack of knowledge about this strain and the fact that it may mutate, some unspecified amount of additional concern is warranted.