Why long COVID brain fog seems so much worse in the U.S.

• A large study of more than 3,100 people is the first to directly compare long COVID brain symptoms across multiple continents
• Brain fog was reported by 86% of non-hospitalized patients in the U.S., compared with just 15% of patients in India
• Researchers found that long COVID symptom patterns were linked more closely to income level than to geographic location
• The striking differences are most likely driven by culture and access to healthcare, rather than differences in the virus itself

Long COVID Brain Symptoms Vary Sharply Across Countries

People with long COVID in the United States report much higher rates of brain fog, depression, and cognitive problems than patients in countries such as India and Nigeria, according to a large international study led by Northwestern Medicine.

Researchers caution that these differences do not necessarily mean Americans experience more severe illness. Instead, the higher symptom burden reported in the U.S. may reflect greater access to neurological and mental health care, along with lower stigma around discussing cognitive and emotional symptoms.

First Cross-Continental Comparison of Long COVID Neurology

The research represents the first study to directly compare neurological symptoms of long COVID across continents. Scientists followed more than 3,100 adults with long COVID who were evaluated at academic medical centers in Chicago; Medellín, Colombia; Lagos, Nigeria; and Jaipur, India.

Most participants were not hospitalized during their initial COVID infections. Within this group, 86% of U.S. patients reported experiencing brain fog. By comparison, brain fog was reported by 63% of patients in Nigeria, 62% in Colombia, and just 15% in India.

Mental health symptoms followed a similar pattern. Nearly 75% of non-hospitalized patients in the U.S. reported depression or anxiety. In Colombia, that figure dropped to about 40%, while fewer than 20% of patients in Nigeria and India reported similar distress.

Cultural Attitudes Shape Symptom Reporting

"It is culturally accepted in the U.S. and Colombia to talk about mental health and cognitive issues, whereas that is not the case in Nigeria and India," said Dr. Igor Koralnik, senior study author and chief of neuro-infectious disease and global neurology at Northwestern University Feinberg School of Medicine.

"Cultural denial of mood disorder symptoms as well as a combination of stigma, misperceptions, religiosity and belief systems, and lack of health literacy may contribute to biased reporting. This may be compounded by a dearth of mental health providers and perceived treatment options in those countries."

The study was published today (Jan. 28) in Frontiers in Human Neuroscience.

Key Neurological Findings Across All Regions

Across every country studied, the most frequently reported neurological symptoms included brain fog, fatigue, myalgia (muscle pain), headache, dizziness, and sensory disturbances (such as numbness or tingling).

Sleep problems also varied widely. Nearly 60% of non-hospitalized U.S. patients reported insomnia, compared with roughly one-third or fewer of patients in Colombia, Nigeria, and India.

When researchers analyzed symptom patterns statistically, they found a clear divide between high- and upper-middle-income countries such as the U.S. and Colombia and lower-middle-income countries such as Nigeria and India.

How the Study Was Conducted

The observational study enrolled adults with ongoing neurological symptoms following COVID-19 infection between 2020 and 2025. Participants were recruited from four academic medical centers and included both hospitalized and non-hospitalized patients.

Symptoms were evaluated using standardized neurological, cognitive, and quality-of-life assessments available at each site, allowing researchers to compare results across regions.

Why Long COVID Remains a Global Concern

Long COVID affects millions of people worldwide and is defined by symptoms that continue for weeks or even years after an initial COVID infection. Estimates suggest that 10-30% of adults who contract COVID develop lasting symptoms, with cognitive and neurological issues among the most disruptive.

As the authors write, long COVID "affects young and middle-aged adults in their prime, causing significant detrimental impact on the workforce, productivity and innovation all over the world."

In this study, patients in the U.S. consistently reported the greatest neurological and psychological burden, which "affected their quality of life and ability to work," according to Koralnik, who also serves as co-director of the Comprehensive COVID Center at Northwestern Medicine and leads the global neurology program at the Havey Institute for Global Health at Feinberg.

What the Findings Mean Going Forward

The researchers say their results highlight the importance of culturally sensitive screening tools and diagnostic approaches for long COVID. They also point to the need for healthcare systems that can support long-term care and follow-up.

Building on these findings, Koralnik and his international collaborators are now testing cognitive rehabilitation treatments for long COVID brain fog in Colombia and Nigeria. These studies use the same treatment protocols developed for patients at the Shirley Ryan AbilityLab in Chicago.

The study is titled "A cross-continental comparative analysis of the neurological manifestations of Long COVID."