One theory is that 60-80% of those in South Africa already had COVID or were vaccinated, and that those who were getting infected had milder cases as a result of their previous exposure or vaccination, AND because in general they were all much younger -- lots of kids and younger adults. That age group is known to be less affected.

The evidence from the UK is that Omicron is every bit as lethal as Delta, it's just a lot more contagious.

No one has any idea what the future holds. Will it mutate to be less lethal? Maybe. Will it mutate to be more lethal? Maybe.