For Mirabai Nicholson-McKellar, Covid-19 brought an onslaught of symptoms from chest pains to an 11-day migraine, three positive test results, and a period in hospital.
Seven months later, the rollercoaster is far from over: the 36-year-old from Byron Bay, Australia is still experiencing symptoms – including difficulties with thinking that are often described as “brain fog”.
“Brain fog seems like such an inferior description of what is actually going on. It’s completely crippling. I am unable to think clearly enough to [do] anything,” says Nicholson-McKellar, adding that the experience would be better described as cognitive impairment.
The consequences, she says, have been enormous.
“I can’t work more than one to two hours a day and even just leaving the house to get some shopping can be a challenge,” she says. “When I get tired it becomes much worse and sometimes all I can do is lay in bed and watch TV.” Brain fog has made her forgetful to the point that she says she burns pots while cooking.
“It often prevents me from being able to have a coherent conversation or write a text message or email,” she adds. “I feel like a shadow of my former self. I am not living right now, I am simply existing.”
Nicholson-McKellar is far from alone.
Dr Michael Zandi, a consultant at the UCL Queen Square Institute of Neurology , says he has seen patients who have been living with brain fog for a few months. While some have been admitted to hospital or intensive care with Covid, Zandi says he is now seeing cases among people who coped with Covid at home.
“The proportion of people with cognitive symptoms for any period of time as a result of Covid-19 is unknown, and a focus of study now, but in some studies could be up to 20%,” he says.
One difficulty in tackling “brain fog” is that the term itself is hazy.
“It is not a medical term, this is what people are putting out there,” says Dr Ross Paterson of the Queen Square institute. “We haven’t defined what these symptoms are and whether they [are] anything measurable because, quite simply, nobody has done the study yet.”
Zandi agrees that difficulties with thinking and concentration have previously been reported by patients with other conditions, including the auto-immune disease lupus.
“Doctors and scientists wouldn’t necessarily use [brain fog] as a diagnosis as it doesn’t exactly tell you what the problem is and what could be causing that,” says Zandi.
Dr Wilfred Van Gorp, former president of the American Academy of Clinical Neuropsychology, says many Covid survivors he has seen with brain fog also have problems ranging from headaches to difficulties tolerating loud noise and controlling emotions.
“The complaints are very much similar to [those of] post-concussion patients,” he says, adding that there are also similarities to chronic fatigue syndrome.
Zandi says there could be many causes of brain fog in Covid survivors, from inflammation in the body to a lack of oxygen to the brain – the latter is a particular concern for those who spent time on ventilators.
Zandi adds that experiments in lab dishes have even suggested the virus can infect brain cells and choke off oxygen delivery to adjacent cells – although that work has yet to be peer-reviewed.
And Paterson says that while studies are small, there is evidence from Covid patients hospitalised with severe neurological syndromes that the coronavirus can affect the nervous system, with concerns it could be causing problems such as neuro-inflammation and damage to the protective coating of nerve cells.
There could be psychological factors, too, particularly among Covid survivors who spent time in intensive care. “That is a very frightening thing to have gone through,” says Zandi.
Dr Nick Grey, a consultant clinical psychologist at Sussex Partnership NHS Foundation Trust said terms similar to “brain fog” have previously been used in connection with extreme tiredness, low mood and conditions such as post-traumatic stress disorder (PTSD) – the latter of which is thought to affect about a quarter of Covid survivors who were in intensive care.
And there is another possibility, says Paterson.
“Are people who have been ill, locked away, more anxious, maybe not sleeping well – are they just more prone to being in a migrainous state?”
Grey stresses that both psychological and biological mechanisms could potentially be at play.
“You are going to need quite careful studies to tease apart what is going on there,” he says.
Scientists have already formed a partnership – dubbed CoroNerve – to explore the neurological and neuropsychiatric complications of Covid-19, while in other work Paterson and colleagues are looking at blood and spinal fluid collected from Covid patients who were hospitalised with neurological symptoms, those who had Covid without such problems, and healthy individuals.
The aim of the new work, he says, is to explore whether even those without neurological symptoms show markers of neurological damage, and to what extent any processes are ongoing.
Like Nicholson-McKellar, Melanie Montano, 32, from New Jersey, in the US, is part of the Body Politic Covid-19 support group on the social media site Slack and tested positive for Covid in March.
About two weeks after her symptoms began, brain fog set in, hampering her work as a writer and educator and leaving her struggling to articulate thoughts or remember details. That, Montano says, is a particular problem as she is applying for a new job.
“I’m just existing in this haze-like frame of mind in which I’m constantly on autopilot,” she says.
Van Gorp says that at present there is little research into brain fog, but suggests exercises to improve cognitive function may help, as might drugs such as the ADHD medication Ritalin.
Others also say there is cause for hope.
“What we don’t know is how long it will go on for,” says Zandi. “But we have seen patients who get better and are functioning.”