Omicron is not relevant to the part of the exchange you are quoting. Still, do you think it will not work against Omicron? If so, why? At any rate, they can always make an Omicron-killed-virus vaccine if they needed to.Omicron, anyone?Before Delta, but after Alpha, Gamma and Lambda, and it still worked against those. So, it does work against variants - at least, against those that were around when the study was carried out. Do you think it would not work against Delta? Well, now Delta is here, and fatalities continue to fall, and as far as one can tell, it continues to work. Sure, you could say they fall for another reason, and it does not work anymore. But do you have evidence of that?
Omicron is derived from the Wuhan strain, not from Delta. Thus "natural" immunity from Delta infection very well might not protect against it.