I like to dive into techy rabbitholes when something sparks an interest. I looked at zoonotic diseases at the biochemmy level a while ago (the ones which can transfer to humans from animals). Covid was remarkably well suited to takeup by humans. Fortunately it wasn't very potent.
Comparable fatality rate for Covid 19 is officially 0.5-1%, where iirc SARS-1 was 3%, Spanish flu 3% and MERS 30%. Ordinary flu 0.1% or so. The numbers are nowhere near as meaningful as they might appear, for various reasons. IFR vs CFR, age ranges, partial exposure history, R numbers and on and on.
If you look at the "possibles", from things like bats, though, it makes you wonder how our species has survived. There are loads which it's thought would be up around 90-95% fatality rates. No problem, as long as:
• they don't transmit to humans and
• if they do, they can't transmit
between humans Airborne, really.
So far the bad bat ones don't do either.
Of the people who have contracted bird flus H5 or H7 ( ~800+ last I saw), death rate is about 55%. You have to get down and dirty to contract it though, it was believed with haughty confidence until recently. There are hundreds of cases of it transmitting in the wild to all sorts of animals, terrestrial and aquatic. Foxes, bears, pumas, seals — a dozen + species.. Thousands in mustilids ( weasley ferrety minky things), where we hope a lot, that they got it from the same source and not from each other..
And guess what, a Dutch lab has modified H5N1 so it
will transmit between mammals too. Wonderful. Lets hope they don't want to make themselves really really famous.
I haven't looked any of that up recently so some will be out of date or just, out.
There
are human vaccines - see
https://en.wikipedia.org/wiki/H5N1_vaccine.
Much muttering about development of testing etc. Likely, I'd have thought, for farmers and that.