More dangerous infection often kill their hosts before they can infect many others, so might result in horrendous dead toll locally but might find it hard to spread very far.

My understanding is that it isn't the death rate that makes this different but how long it incubates for, allowing it to spread much further. The death rate could have been much higher and we'd probably still end up with a pandemic.

I actually think its' success is largely due to the low mortality rate.

At the extreme if it killed 100% of the people it infected then everyone would've locked down borders immediately and taken it very seriously.

But instead it's only 10x as deadly as a common virus (the flu) that most people have personally had. Which made people not very wary of it until they saw the exponential spread problem illustrated in Italy. (China also illustrated that but Westerners really only feel something can personally affect them if it happens to other Westerners)

> At the extreme if it killed 100% of the people it infected then everyone would've locked down borders immediately and taken it very seriously.

Depends on how fast it kills too. Something like airborne aids that somehow didn't have respiratory symptoms would be the most terrifying scenario because it would spread world wide before anyone noticed.