It's still early but here's an example of what it's looking like:

https://www.medrxiv.org/content/10.1101/2021.12.27.21268278v...

> Our results show that the Omicron VOC is generally 2.7-3.7 times more infectious than the Delta VOC among vaccinated individuals (Table 3). This observation is in line with data from (18), which estimated that 19% of Omicron VOC primary cases in households in the UK resulted in at least one other infection within the household, compared to only 8.3% of those associated with the Delta VOC. Furthermore, we show that fully vaccinated and booster-vaccinated individuals are generally less susceptible to infection compared to unvaccinated individuals (Table 2). We also show that booster-vaccinated individuals generally had a reduced transmissibility (OR: 0.72, CI: 0.56-0.92), and that unvaccinated individuals had a higher transmissibility (OR: 1.41, CI: 1.27-1.57), compared to fully vaccinated individuals.

> Surprisingly, we observed no significant difference between the SAR of Omicron versus Delta among unvaccinated individuals (Table 3). This indicates that the increased trans-missibility of the Omicron VOC primarily can be ascribed to immune evasion rather than an inherent increase in the basic transmissibility.

That last part is why the boosters matter: neutralizing antibodies (which your body stops producing over time after the infection) can prevent someone from getting sick at all, whereas the longer-lasting T cell response helps your immune system fight it off more effectively. If the entire population is boosted, that would have been plenty to fight off Delta but with Omicron we still need a combination of other measures (masks, air filtering/exchange, etc.) and eventually updated boosters to put an end ot it. That doesn't mean that being vaccinated isn't worthwhile, of course: you're still far more likely to have a better outcome if you get it and the window where you're contagious is smaller.

I encourage everyone eligible to protect themselves by getting vaccinated but we're really chasing our tails by focusing on antibody levels. In the long run cellular immunity is more important. We can't give everyone boosters every few months just to keep antibody levels up.

https://youtu.be/GklHGYY8vN8

We can't put an end to this virus. It will be around at some level forever.

That's why the different between the neutralizing antibodies and T cells is so important: when the pandemic is raging, your odds of exposure are high and so public health people are concerned about the ability of vaccinated individuals to slow the spread impacting the entire healthcare system. The medical system is under levels of stress which haven't been seen in a century so they're understandably focused on trying all of the tools available to calm things down.

Once it's spreading at a lower level, your risk of personal exposure is much lower and the long-lasting T cell response becomes more of a focus because that reduces risk to the person and you're less worried about the crunch of many thousands of people showing up at the hospital at the same time because for someone vaccinated it's more like something like influenza where most people have a bad week or two but don't urgently need medical treatment.