But the ratio of cases to hospitalisations to deaths has changed with vaccines (as Boys3 brilliant data charts often show) and I think that is what the media are trying to say
No, there has been many saying that omicron is less serious in South Africa - the number of people in hospital in South Africa has dropped significantly since the cases started rising, we don't actually know if this is due to different lag, 'cos it's re-infection and protection against severe outcomes are there, or something about the demographic being infected (remember SA is a young population and has already had excess deaths, there may not be many left to be seriously harmed)
But so far, since mid November, people in hospital in SA with Covid has dropped by 1/3rd - even as admissions has stayed within the same ballpark - ie people are discharged at a faster rate in the last weeks. But of course it is too early to actually be confident of these figures - but it's that not vaccines that people are talking about and the twitter "thread" was talking about.