Different countries, different demographics, different social interactions, different accommodation, different infection profiles, different behaviours. You can’t directly compare SA with the UK.
The UK has some of the very best best tracking and monitoring in the world. There is huge certainty that omicron will race through our population in very, very short order (doubling rate of less than 2 days). Omicron has barely got started but just yesterday there was a huge jump (that was on line with current predictions)
Even if it is less severe (still not certain) you can get into health care supply issues very quickly indeed.
Because of the speed of transmission you cannot wait for certainty of severity to act.
Simple maths, if you have ten times the number of infections for a disease that is only a third as likely to put you in hospital but those hospitalisations are compressed into a very short period of time, you have problems.
That’s why the booster program has been turbo-charged. By the end of the week we’ll have about 50% of the population boosted and that initial 50% should cover the most vulnerable. Hopefully that should make a big difference but we’ll see.