The Omicron variant doesn't cause as much severe illness as other variants have, but its "mild" symptoms can still be pretty unpleasant.

The big picture: The way health care professionals and doctors differentiate between "mild" and "severe" illness may not align with a layperson's understanding of those terms.

"To a health care professional, 'mild' means you're not getting hospitalized," said Megan Ranney, academic dean at the Brown University School of Public Health.

• But, she said: "Omicron symptoms can range from absolutely no symptoms to a really mild cold to something where you are in bed with shakes and chills, and have a horrible cough and are fatigued and headachy for weeks. Those are all 'mild.'"
• A "severe," illness means you'd likely have symptoms such as very low oxygen levels, kidney damage and heart impairment, she said.

What we're watching: Omicron is causing a lot less severe illness than previous variants, but a "mild" case can still require about a week away from work, especially in front-line jobs.

• And because so many people have gotten infected in such a short time, it's leaving schools, airlines, and other businesses — including, critically, hospitals — with large numbers of workers out sick simultaneously, The Atlantic reported.
• Then there's the matter of long COVID. A study published Thursday in Nature Immunology found ongoing, sustained inflammatory responses following even mild-to-moderate COVID-19 cases.

What they're saying: "It's going to be a messy few weeks. I don’t think there’s any way around it," said Joseph Allen, a professor of public health at Harvard, per The Atlantic.