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'Brain Fog' After COVID-19: Many Mild Cases Leave Lasting Impact, Study Finds

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A new study from UCSF researchers suggests 'brain fog' may be more common among patients who had milder cases of COVID-19 and rode their illness out at home. 'They were in their late 30s, as an average age,' said a researcher. (Getty Images)

It’s been almost a year since he had COVID-19, and Bruce Wheeler is still struggling with lingering symptoms, like the headaches that come not just once in a while, but every day for the last seven months.

"It would just feel like there's a knife in my temple, just burning,” he says. “I can get up at eight o'clock in the morning and by 9:30 or 10:00 a.m. I'm back in bed because my head is pounding.”

Wheeler also tires easily. The 74-year-old used to hike in the Alps, but now he can barely make it up the stairs in his house without huffing and puffing. But the thing that really bothers him is what people are calling “brain fog.” He gets disoriented, he can’t focus and he forgets things — and it's not just once in a while. It happens multiple times every day.

“I'll go into the kitchen wanting to get something out of the refrigerator and I open a cabinet,” Wheeler says. “I forget what I'm there for and I’ve gone to the wrong place.”

He’ll watch a movie with his wife and the next morning, he can’t remember what he saw. Even in the moment he’s staring at Russell Crowe on screen, he can’t remember his name.

“And then there's another Australian actress that's in every movie? Do you know the most popular Australian actress?” Wheeler asks me during an interview.

"Nicole Kidman," I say.

“Nicole Kidman,” Wheeler confirms. “Whenever I see them or think of them, I just have a gap. Sometimes it’s very obvious things, sometimes it's somebody who's very important in my life, I just can't remember their name.”

Bruce Wheeler hikes in England in 2017. Since he got COVID-19 in March 2020, he's had a hard time walking long distances or up hills — but what really bothers him is what people are calling 'brain fog.' (Courtesy Dale Wheeler)

These kinds of persistent cognitive problems have so far been documented mainly among older people who had to be hospitalized for severe cases of COVID-19.

But Wheeler was never in the hospital.

A new study from UCSF researchers suggests brain fog may be more common among patients like Wheeler who had milder cases of COVID-19 and rode their illness out at home. Out of 100 patients tracked, 20 experienced cognitive issues and 14 of them had never been in the hospital.

“We looked at the demographics of these individuals — they were overwhelmingly young,” says Joanna Hellmuth, a cognitive neurologist at UCSF and lead author of the study. “They were in their late 30s, as an average age.”

This is problematic, she says, because most tools used to screen for cognitive issues were designed to detect dementia.

“We have a lot of limited ways that our society thinks about thinking and memory changes. It’s either dementia or it's nothing,” she says. “There's really no in between in these more subtle cognitive disorders that really aren't recognized as much in the medical field.”


Scientists aren’t sure what causes COVID-19-related brain fog. They theorize it may be brain damage caused directly by the virus, or it could be an indirect result of the body’s immune response in fighting the virus. As a result, doctors aren’t sure how to treat it. They don’t know how long it might last and when, or if, the symptoms will go away.

Research has been limited. Most studies have been among patients who were hospitalized, Hellmuth says, because they are conducted mainly by ICU doctors who follow their own patients after discharge.

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Hellmuth and her team want to study the 85% of COVID-19 patients who were never hospitalized. While the new UCSF study is small, she says, it documents cognitive changes in outpatients in detail and opens the door for other researchers to do more, bigger studies.

This is needed to understand the long-term economic and societal impacts of COVID-19 illness, she adds.

“There are a lot of working people who had COVID-19 who aren't able to do their jobs like they used to,” she says. “I've had a number of people ask me to write notes for work to legitimize their cognitive issues. I've had patients in their teens and I've had to write notes to their school.”

For Bruce Wheeler, his symptoms became so bad he couldn’t track conversations or group Zoom calls and he had to step back from the volunteer work he does for local museums and nonprofits. The hardest part of brain fog, he says, is the emotional toll it takes, the stress and guilt of forgetting.

"Six months ago, it really got me down. Now I kind of accept it in myself," he says. "Being able to make light of it at times, have a laugh with family or friends, ‘C’mon, Bruce, Try harder! Who is that Australian actress?'"

He pauses.

“No, I can't remember. You gave it to me, what, five minutes ago?” he says, looking up at me.

"Nicole Kidman," I say.

“Nicole Kidman,” he sighs. “Damn.”

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