Researchers cautioned that the higher symptom burden reported in the U.S. may reflect lower stigma and greater access to neurological and mental healthcare services, rather than more severe disease.

The study — the first cross-continental comparison of neurological manifestations of long COVID — tracked more than 3,100 adults evaluated at academic medical centers in Chicago (U.S.); Medellín (Colombia); Lagos (Nigeria); and Jaipur (India).

Among patients who were not hospitalized during their initial COVID-19 infection — the majority in the study — 86% in the U.S. reported experiencing brain fog. In contrast, the figure was 63% in Nigeria, 62% in Colombia and just 15% in India.

A similar pattern emerged for psychological distress. Nearly 75% of non-hospitalized U.S. patients reported symptoms of depression or anxiety, compared with about 40% in Colombia and fewer than 20% in Nigeria and India.

“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 author of the study and chief of Neuro-infectious Disease and Global Neurology at Northwestern Medicine.

He noted that cultural stigma, denial of mood disorder symptoms, religiosity, misperceptions and limited health literacy may contribute to underreporting in some countries. A shortage of mental health providers and limited access to treatment options may further compound the issue.

Key Findings

Across all four countries, the most commonly reported neurological symptoms included brain fog, fatigue, muscle pain (myalgia), headache, dizziness and sensory disturbances such as numbness or tingling.

Insomnia was reported by nearly 60% of non-hospitalized patients in the U.S., compared with roughly one-third or fewer patients in Colombia, Nigeria and India.

Statistical analysis showed a clear separation in symptom reporting between high- and upper-middle-income countries (U.S. and Colombia) and lower-middle-income countries (Nigeria and India).

Study Design

The observational study enrolled adults between 2020 and 2025 who experienced persistent neurological symptoms following COVID-19 infection. Participants included both hospitalized and non-hospitalized patients. Researchers used standardized neurological, cognitive and quality-of-life assessment tools available at each study site.

Understanding Long COVID

Long COVID affects millions worldwide and is characterized by symptoms that persist for weeks, months or even years after acute infection. Studies estimate that between 10% and 30% of adults infected with COVID-19 develop long-term symptoms, with neurological and cognitive complaints among the most common and debilitating.

The condition often affects young and middle-aged adults in their prime working years, leading to significant impacts on productivity, workforce participation and overall quality of life.

In the current study, U.S. patients consistently reported the highest burden of neurological and psychological symptoms, which researchers said significantly affected their ability to work and daily functioning.

What’s Next

The authors emphasized the need for culturally sensitive screening tools and diagnostic frameworks for long COVID. They also highlighted the importance of strengthening healthcare systems to provide long-term follow-up care.

Building on these findings, Koralnik and his international collaborators are now studying cognitive rehabilitation therapies for long COVID-related brain fog in Colombia and Nigeria, using protocols developed at the Shirley Ryan AbilityLab in Chicago.