Brain fog in long COVID

As hundreds of millions of people have been infected with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) over the past two years, persistent symptoms have plagued a large proportion of recovered cases. This condition, which has otherwise been referred to as ‘long coronavirus disease 2019 (COVID-19),’ is associated with a myriad of apparently unrelated symptoms that can lead to a decline in productivity, inability to carry out daily activities, depression, and a decreased quality of life.

A new Journal of Medical Virology study explores one troubling manifestation of this condition, which is the cognitive impairment that follows clinical resolution of COVID-19.

Study: Long COVID Syndrome-Associated Brain Fog. Image Credit: Good Studio /


Apart from the daily risk of serious disease and death from COVID-19, it has become clear that many people who have recovered from the acute infection, even those who had mild cases, suffer from lingering symptoms for weeks to months thereafter. Also called the post-COVID syndrome, long COVID is defined by the National Institute for Health and Clinical Excellence, the Scottish Intercollegiate Guidelines Network, and the Royal College of General Practitioners as: “signs and symptoms that develop during or after an infection consistent with COVID-19, continue for more than 12 weeks, and are not explained by an alternative diagnosis.”

Brain involvement in COVID-19 is possible as a result of encephalitis, strokes, or more subtle injuries that affect the attention span and ability to carry out tasks that require thinking. The result of the latter type of damage is called brain fog and causes the affected patient to feel mentally slow or fuzzy.

The current study looks at how often this syndrome is seen and its potential risk factors.

Study findings

In a large sample of approximately 2,700 COVID-19 patients, with a mean age of 41 years, neurological symptoms were found in about a fifth of them at admission. This included disorientation, headache, and anosmia.

Upon follow-up, about two-thirds of the patients had chronic symptoms, with brain fog being specifically reported in 7%. Some factors were more common in these patients.

More females reported feeling fuzzy for weeks to months after recovery at a ratio of 1.1 females to every male. Brain fog was also more common in those who presented with respiratory symptoms at the outset, at 93% to 88% of those who had other symptoms.

Patients who were admitted to the intensive care unit (ICU) were also more likely to experience brain fog during and after convalescence, at 14% versus 8% of non-ICU patients.


The number of papers on long COVID is large and increasing; however, there is a significant lack of clarity on the impact of these conditions and the risk factors for its development. In the current study, up to 62% of patients had chronic symptoms fitting the criteria for long COVID, despite being young adults with an average age of 41 years.

About 7% of the patients in this study complained of being unable to think and process information properly, along with difficulties with attention, which is often called brain fog. Earlier research has shown similar trends, but with higher proportions of this syndrome. The differences may be due to variations in the methods used.

Specifically, leading questions elicit a higher rate of response regarding this syndrome. In contrast, people without this side effect tend to respond to general surveys more often. The use of cognition tests also tends to produce a higher rate of case detection than relying on self-reported brain fog.

It is becoming obvious that even mild COVID-19 can be followed by brain fog and other neurological symptoms. The associated decline in the quality of life and productivity makes it a significant issue to be dealt with by medical researchers and healthcare professionals.

The feasibility and cost-effectiveness of active screening for all COVID-19 convalescents early on support its implementation into current treatment protocols. The risk factors identified in this study show important predisposing factors.

Females seem to have a slightly higher incidence, a fact that requires further exploration of the underlying mechanisms. Since ICU patients tended to have almost twice as high a risk of this syndrome as others, the severity of the disease may also play a role.

The mechanisms by which brain fog associated with long COVID develops may include brain damage by the high levels of circulating cytokines and inflammatory mediators, the adverse effects of the various medical treatments used in severe or critical COVID-19 including intubation, as well as hospital-acquired infections that may leave chronic imprints on the patient’s health. SARS-CoV-2-associated changes in brain areas are also implicated in cognitive processing like the cingulate cortex.

The evidence presented here suggests that brain fog is not, as many medical professionals have suggested, ‘all in the mind’ of the patients, but is a real biological phenomenon. Another line of thinking attributes this adverse effect to the psychological and social factors that play a role during the infection and recovery; however, this must be further explored.

It is indubitable that patients who have recovered from COVID-19 continue to suffer from impaired physical and mental functioning, anxiety, insecurity about employment, depression due to weakness and the inability to contribute at home and/or the workplace, and sleep disturbances for up to six months. The need for guidelines to diagnose, monitor, and treat these symptoms and avoid permanent or chronic cognitive impairment is apparent.

Further work will be needed to estimate the rate of such symptoms after an asymptomatic or mild infection, as well as over a longer period, with comparison groups included in the study.

Journal reference:
Dr. Liji Thomas

Written by

Dr. Liji Thomas

Dr. Liji Thomas is an OB-GYN, who graduated from the Government Medical College, University of Calicut, Kerala, in 2001. Liji practiced as a full-time consultant in obstetrics/gynecology in a private hospital for a few years following her graduation. She has counseled hundreds of patients facing issues from pregnancy-related problems and infertility, and has been in charge of over 2,000 deliveries, striving always to achieve a normal delivery rather than operative.


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