The winter Omicron wave is coming — quickly

Data flooding in from South Africa and Europe is clear: The Omicron variant is spreading extremely quickly, including among vaccinated people.

Why it matters: If this trend holds up, that means a lot of people — around the world and in the U.S. — are about to get sick, even if only mildly so.

Driving the news: An early estimate published yesterday by the UK found that two doses of the Pfizer vaccine are only about 30% effective against symptomatic infection with Omicron, and the AstraZeneca vaccine isn't effective at all.

• A booster shot of the Pfizer vaccine, however, increases effectiveness to 70-75%.
• Experts expect the vaccines to retain higher levels of effectiveness against severe disease, although this hasn't yet been measured.
• Compared to the Delta variant, the risk of reinfection with Omicron is three to eight times higher. This level of immune escape is part of why the variant's transmission has also spiked.

Between the lines: Researchers are estimating that it's taking only between two and three days for the number of Omicron cases to double — meaning it's spreading incredibly fast.

• The UK report estimates that "if Omicron continues to grow at the present rate, Omicron case numbers are projected to reach parity with Delta cases in mid-December."
• The U.S. isn't likely to be too far behind the UK.

Yes, but: In the UK, there are no hospitalizations or deaths associated with Omicron so far.

• Among 43 U.S. cases, only one resulted in hospitalization, the CDC said yesterday.
• That could be because people getting breakthrough infections have milder symptoms, or because the virus overall causes less severe disease, but it's too soon to draw any firm conclusions.

What they're saying: "Omicron would have to be very much milder than Delta, in order to avoid an increase in hospitalisations and deaths," tweeted Meaghan Kall, one of the authors of the UK report.

• "Remember, a small percentage of a big number is still a bigger number than we would like to see."

What we're watching: Only about 26% of vaccinated Americans have received a booster shot, and only 61% of the overall U.S. population is vaccinated, per the CDC.

• If Omicron keeps spreading like it has been, that means U.S. case numbers are also about to skyrocket, save massive behavioral changes.
• The best thing you can do to prepare is get vaccinated or get a booster shot.