The OG Ebola had almost 100% fatality rate, and a short gestation time (I think only a few days). It didn't spread too far. The one that killed a few thousand people, though, had about a 50% fatality rate, and I think its gestation period was a bit over a week (these are the products of a faulty memory, but quoting LLM output isn't considered polite, hereabouts, and, for all we know, they could hallucinate the stats, anyway). Also, a hemorrhagic fever pretty much chews up your organs, so it's likely to drive bad health outcomes, for the rest of our lives, even if we survive.
HIV/AIDS has (the meds just keep it at bay) a 100% fatality rate, but a very long gestation period.
COVID, I believe, had about a 1% rate, in the OG variant, and that brought the world to a standstill. I think Spanish Flu (another world standstill), had about 2.5%, and a relatively short gestation period, but it was also quite communicable.