brain fog

COVID-19 ‘Brain Fog’ is Real and Can Last Over a Year, Dropping IQ As Much As 9 Points

Recent groundbreaking research might change our understanding of the long-term effects of COVID-19, with researchers revealing that even mild cases of the virus can lead to significant cognitive declines, or “brain fog,” including drops in up to 3 to 9 IQ points.  

Conducted by a team of researchers at the Imperial College London, the study stands out as one of the most extensive investigations into the aftereffects of COVID-19. 

Researchers say that findings conclusively demonstrate that the so-called “COVID brain fog”—a term used to describe cognitive impairments following infection—is real. More crucially, research shows these cognitive difficulties can last over a year after the initial infection.

The study results were published in the prestigious New England Journal of Medicine on February 29.

“The potential long-term effects of COVID-19 on cognitive function have been a concern for the public, healthcare professionals, and policymakers,” co-author and Professor of Brain Sciences at Imperial College London, Adam Hampshire, said in a statement. “Until now, it has been difficult to objectively measure them in a large population sample.” 

The study involved over 140,000 participants out of an invited 800,000 adults. This massive scale allowed for a comprehensive analysis of cognitive functions across various dimensions, such as age, demographics, or pre-existing medical conditions.

Participants underwent a cutting-edge online cognitive assessment using the “Cognitron platform.” The platform is designed to identify minor variations in various brain functions, including memory, reasoning, executive function, attention, and impulsivity. Researchers say they could detect subtle shifts in cognitive abilities through this innovative approach.

The results showed that those who have recovered from COVID-19 exhibited measurable cognitive deficits compared to individuals never infected by the virus.

Participants experiencing “Long COVID,” defined as symptoms persisting for more than 4 weeks, showed the most significant cognitive impairments. However, even individuals who experienced short-term or mild cases of COVID-19 also demonstrated slight but significant cognitive impairments. 

Findings revealed that COVID-19 impacts various cognitive functions, particularly memory. Individuals had difficulty recalling images of objects they had seen just minutes before, suggesting an issue with forming new memories rather than an increased rate of forgetting. 

Additionally, minor deficiencies were observed in executive functions and reasoning skills, including spatial planning and verbal reasoning. The results highlight the broad spectrum of cognitive challenges associated with COVID-19.

Researchers say these post-COVID cognitive deficiencies were still detectable a year or more after their initial infection. This finding is particularly concerning, suggesting that the cognitive aftermath of COVID-19 could linger well beyond the resolution of physical symptoms.

These results align with anecdotal accounts from thousands of COVID-19 survivors who have reported suffering from COVID brain fog, including struggles with memory, concentration, and other cognitive challenges long after their initial recovery.

Delving deeper, the study found that there appeared to be differing cognitive impacts based on the variant of the virus. Infections from the original strain or “alpha variant” led to more pronounced cognitive deficits than those from later variants. 

Moreover, hospitalization, particularly ICU admissions, was correlated with even more significant cognitive declines, emphasizing the virus’s potentially severe impact on brain function.

Results showed that the severity of COVID-19 infection also plays a crucial role in the extent of cognitive deficits observed, with varying degrees of impact on IQ levels. 

Participants who experienced milder symptoms, showed a modest drop in cognitive performance, roughly translating to a decrease of 3 IQ points. However, for those with lingering, unresolved symptoms associated with “Long COVID,” the decline doubled to a substantial 6 IQ point drop. The most pronounced cognitive impairments were seen in patients who required ICU admission, experiencing a sharp fall of 9 IQ points. 

Interestingly, the study also observed a temporal dimension to the cognitive effects of COVID-19. Infections earlier in the pandemic, when treatments were scarce and the health system was under immense pressure, showed more significant cognitive impacts than those occurring later, amidst advancements in treatment and the widespread availability of vaccines.

“Our results confirmed associations of cognitive deficits with mood swings and fatigue but also with a variety of other symptoms,” study authors wrote. “Therefore, it is likely that multiple underlying factors contribute to cognitive deficits after Covid-19.” 

While the study indicates that some recovery from COVID brain fog is possible, particularly for those whose symptoms eventually resolve, it also underscores the need for ongoing support and understanding for COVID-19 survivors. 

The persistence of cognitive deficits, especially among those with prolonged symptoms, highlights a crucial aspect of the pandemic’s aftermath that demands attention.

Additionally, these research findings raise questions about the broader societal impact of COVID-19, particularly concerning the workforce, education, and healthcare systems. With millions affected globally, the cumulative effect of these cognitive declines could have far-reaching consequences.

Ultimately, this recent study is a stark reminder of COVID-19’s lingering shadows, even as the world strides toward recovery. It calls for reassessing post-COVID care strategies, emphasizing cognitive rehabilitation and support systems. 

“It is reassuring that people with persistent symptoms after COVID-19, that had resolved, may expect to experience some improvement in their cognitive functions to similar levels as those who experienced short illness,” co-author and Director of the REACT program from the School of Public Health at Imperial College London, Dr. Paul Elliott said. 

“However, given the large numbers of people who were infected, it will be important to continue to monitor the long-term clinical and cognitive consequences of the COVID-19 pandemic.”

Tim McMillan is a retired law enforcement executive, investigative reporter and co-founder of The Debrief. His writing typically focuses on defense, national security, the Intelligence Community and topics related to psychology. You can follow Tim on Twitter: @LtTimMcMillan.  Tim can be reached by email: or through encrypted email: