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I hear a lot of talk in the news these days about the omicron variant and the kind of disease it might cause: mild, moderate, severe. Could you explain those terms?

As the omicron variant spreads around the globe, everyone wants to know: Will it cause mainly mild disease? Moderate? Severe?

Early studies suggest that many people could have asymptomatic or mild cases rather than severe, in part because many more people are now vaccinated or have had previous disease. There's not yet enough data for a definitive answer.

And then there's the question of what exactly "mild," "moderate" and "severe" mean vis-a-vis COVID.

It turns out that question isn't so easy to answer. That's because doctors and patients have different concerns when assessing COVID.

Doctors think in terms of how your lungs and other organs are doing and what treatments might be required.

"SARS-CoV-2 is a respiratory virus that causes COVID, and the designations refer largely to how well a patient's lungs are able to oxygenate and what treatment is necessary to keep the illness from progressing," says Stanford University infectious disease physician Dr. Abraar Karan.

"So when we move from mild to severe, we mean how easy or how difficult is it for you to breathe and maintain certain oxygen levels in your blood, and what treatments, if any, should we be using."

Patients, meanwhile, think in terms of how horrible they might feel. This is an important distinction because some patients can have very low oxygen levels without many other symptoms or could have bad symptoms such as high fever and a painful headache but have normal oxygen levels.

So what does a mild case look like? A mild case could mean barely any symptoms and a quick return to feeling normal. But so-called mild cases aren't always ... well, mild. The National Institutes of Health guidelines for treatment categorize mild COVID as" [i]ndividuals who have any of the various signs and symptoms of COVID-19 (e.g., fever, cough, sore throat, malaise, headache, muscle pain, nausea, vomiting, diarrhea, loss of taste and smell) but who do not have shortness of breath, dyspnea (difficult or labored breathing), or abnormal chest imaging."

"At board of health meetings I've heard discussions of people designated as 'mild' but they couldn't get out of bed for three days," says Shira Doron, a hospital epidemiologist at Tufts Medical Center in Boston.

Indeed, NPR reporter Will Stone had a case of COVID that would be classified as "mild" by the guidelines that Dr. Karan cites. And here's Stone's self-report:

"Fatigue had enveloped me like a weighted blanket...[n]ext, a headache clamped down on the back of my skull. Then my eyeballs started to ache. And soon enough, everything tasted like nothing...It was a miserable five days. My legs and arms ached, my fever crept up to 103 and every few hours of sleep would leave my sheets drenched in sweat."

Not exactly what you think of when you hear the word "mild."

As for moderate, patients in that category would experience shortness of breath or difficulty breathing. If you're using a device called a pulse oximeter to monitor your breathing, you should seek medical attention if the concentration of oxygen in your blood falls below 94%.

To make matters more complicated, the World Health Organization updated its descriptors in November — and they're different than those used by NIH. Rather than mild, moderate, and severe, WHO uses the terms "non-severe" "severe" and "critical." It defines non-severe as "absence of signs of severe or critical disease." Critical disease covers individuals who have respiratory failure, septic shock and/or multiple organ dysfunction.

So what's a patient to do?

First off, Karan urges that anyone with symptoms get tested to see if it's actually COVID-19 you have. It is flu season and other viral and bacterial infections are circulating. If you don't have COVID and your symptoms worsen, you might benefit from a targeted therapy for what you do have, such as a flu antiviral or an antibiotic.

And perhaps you shouldn't worry about figuring out the right adjective for your case, suggests Dr. William Schaffner, professor of medicine at Vanderbilt University and medical director of the National Foundation for Infectious Diseases. It's more important to alert your physician to what you're experiencing, he says.

"Be very specific about symptoms," says Schaffner, "including temperature, any difficulty breathing and your oxygen saturation rate if you are using a pulse oximeter. We need these benchmarks to put people and their doctors on alert that symptoms could be progressing and they need to be seen. And always tell the doctor if you — or someone with you — just have this feeling that things are going south."

One more note on the subject of COVID terminology. Dr. Waafa El-Sadr, chair of global health at the Mailman School of Public Health at Columbia University, has another description she'd like to see made more precise: "breakthrough infections." That's what cases are COVID are called in people who are fully vaccinated — and in some cases boosted.

"We should be saying post-vaccination infections instead," says El-Sadr. "Breakthrough implies the vaccine has failed, when we knew from day one that these vaccines were never expected to protect 100% from developing infections. What they do is decrease the risk of getting infected and of hospitalization."

El Sadr says that just when we need unvaccinated people to go ahead and get their shots, "the term breakthrough may be undermining the importance of being vaccinated and boosted."

Fran Kritz is a health policy reporter based in Washington, D.C., who has contributed to The Washington Post and Kaiser Health News. Find her on Twitter: @fkritz

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