Why NIH Must Not Abandon Brain Fog Research
Long-COVID brain fog affects millions—we need more research, not less.
Posted March 25, 2025 | Reviewed by Michelle Quirk
Just a few months into the new U.S. president’s term, major changes are occurring in how the government’s main biomedical research agency, the National Institutes of Health (NIH), allocates funding.
I am hoping that, as the single biggest funder of long COVID research , NIH continues to fund at least one critical area: “ brain fog ,” a debilitating symptom of long COVID and other infectious diseases. Here's why.
“Brain fog” is not a formal medical diagnosis. Rather, it is a term widely used by researchers, patients, and the media to describe a combination of symptoms, including the following:
People with brain fog often describe feeling like they are in a haze, their thinking sluggish or disorganized. Studies have shown measurable changes in cognitive performance in patients experiencing these symptoms.
Currently, there is no single test for brain fog. Healthcare providers diagnose the condition and researchers classify cases using the symptoms that patients report, neurocognitive assessments, and functional MRI to detect changes in brain activity.
The only treatments currently available include symptom management through cognitive rehabilitation, physical exercise, sleep optimization, and medications that target specific deficits like fatigue or attention problems.
The Link Between COVID-19 and Brain Fog
As of September 2024, an estimated 17.9 million Americans likely had long COVID, and symptoms are thought to last for months to years. The risk is highest in people in whom the acute infection is most severe .
Brain fog is one of the most common and debilitating symptoms of long COVID. Individuals with long COVID are more likely to show deficits in memory, attention, and processing speed, even in cases where the initial infection was mild. Brain fog can also significantly impact daily life, limiting a person’s ability to work, study, or engage in social activities. COVID-19 vaccines have been shown in high-quality studies done both in the United States and other countries to reduce the likelihood of developing brain fog and long COVID.
What Causes Brain Fog in COVID-19?
The leading theory for COVID-19-related brain fog is neuroinflammation —an immune response in the brain triggered by viral infection. Researchers believe that there are a few possible mechanisms for how the virus damages brain cells:
Do Other Viral Infections Cause Brain Fog?
While COVID-19 has brought more attention and research into brain fog, a similar syndrome occurs with other infectious diseases. Infection with H1N1 influenza was observed to cause cognitive impairment similar to those seen in COVID-19, including brain fog. Many other respiratory viruses can also cause central nervous system problems.
West Nile virus and other viral causes of encephalitis cause direct infection of the brain, leaving some survivors with long-term depression , memory loss, and motor dysfunction. Even with effective antiretroviral therapy , up to 40 percent of HIV-infected people develop cognitive impairment, likely due to chronic inflammation and persistent low-level viral activity in the brain.
Brain fog has also been reported following Epstein-Barr virus (which causes mononucleosis), Lyme disease, and even some cases of dengue fever. The common thread is believed to immune system activation and inflammation that persist long after the acute infection has resolved.
W hy We Need to Keep Researching Long COVID Brain Fog
There are two main reasons I hope that NIH continues to fund research into long COVID.
First, COVID-19 is now a regular part of our seasonal virus landscape, which means that more people will continue to develop this debilitating condition.
Second, understanding brain fog from COVID-19 infection will help us understand all the other ways in which viruses cause inflammation in the brain, potentially giving us treatment for those conditions or related neurologic conditions that are associated with inflammation.
Here are some key questions that we still do not have complete answers to:
Why Continued NIH Funding Matters
Past research on post-viral syndromes, such as chronic fatigue syndrome, has often been dismissed or underfunded until overwhelming evidence forced action. The COVID-19 pandemic has given scientists an unprecedented opportunity to study this problem. If we stop this work now, we risk missing an opportunity to help people who are suffering now and people who will suffer in the future.
NIH reels with fear, uncertainty about future of scientific research. Washington Post. March 5, 2025.
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Jay K. Varma, M.D., is a physician and epidemiologist with expertise in the prevention and control of infectious diseases. He is formerly with the Centers for Disease Control and Prevention.
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This article is part of the Bringwise Psychology Journal — daily insights on human behavior, mental health, and personal growth.