Yes, omicron has overtaken delta/ USA Today

From USA Today, information from South Africa on Omicron, with reporting by Karen Weintraub, a superb reporter, whose book on Lyme disease, Cause Unknown, is excellent.

"...Only 2% to 4% of infected people are ending up in hospitals, compared with about 20% during the beta and delta waves, Karim said. Before, two-thirds of those hospitalized had severe cases; now about one-quarter meet that criteria. Death rates are one-tenth as high as they were with previous variants.

"The clinical picture we are seeing is one of substantially less severe disease," he said.

Karim said he doesn't have information on how many hospitalized patients had been previously infected or vaccinated, though he expects to get that soon.

Anecdotally, Karim said, "there's a preponderance of unvaccinated" in hospitals, probably about 75% of patients. "Is it more severe in that group? What's the picture? I can't tell at this point because I don't have that data."

Note that the majority of South African adults are unvaccinated. 

... Unlike other variants, which slowly made their way from country to country, omicron is exploding around the world simultaneously, said Jacob Lemieux, an infectious diseases staff physician at Massachusetts General Hospital.

"In prior waves, we had a few weeks to watch what was happening in Western Europe and other places to know what we were in store for," he said. Not this time. "We're not going to have the luxury of watching what's going to unfold in our country elsewhere in advance."

The reason is that nobody was looking as it spread. 

WaPo update, 12/22/21 5 pm:

The massive wave of omicron variant infections in South Africa is subsiding quickly. Just a week ago, the country was seeing soaring positivity rates and long lines for testing. Now, cases are dropping sharply. It's hopeful news from the first country to detect the new pathogen, but it's too early to tell whether omicron will follow the same course in the United States and the rest of the world. South Africa's population skews younger than the U.S. population, and some 70 percent of South Africans had already been infected with other variants, meaning many people had some protection through natural immunity.