COVID-19 patients in the United States report “brain fog,” depression, and cognitive difficulties significantly more often than patients in India or Nigeria. This conclusion comes from a large international study led by experts from Northwestern Medicine, published in the journal Frontiers in Human Neuroscience (FHN).

This is the first intercontinental comparison of neurological manifestations of COVID-19. The study included more than 3,100 adult patients evaluated at academic medical centers in Chicago (USA), Medellín (Colombia), Lagos (Nigeria), and Jaipur (India). Both hospitalized and non-hospitalized patients who had COVID-19 between 2020 and 2025 were analyzed.

Among patients who were not hospitalized during the acute infection, 86% of participants in the U.S. reported experiencing “brain fog.” In comparison, the rates were 63% in Nigeria, 62% in Colombia, and only 15% in India. Similar differences were observed for psychological symptoms: nearly 75% of American patients reported depression or anxiety, compared with about 40% in Colombia and less than 20% in Nigeria and India.

According to the study’s senior author, Igor Koralnik, head of Neuroinfectious Diseases and Global Neurology at Northwestern University Feinberg School of Medicine, the higher symptom burden in the U.S. may reflect cultural and systemic differences rather than more severe disease.

“In the U.S. and Colombia, discussing mental health and cognitive issues is socially acceptable, whereas in Nigeria and India it is not. Stigma, religious beliefs, low health literacy, and limited access to mental health professionals may lead to underreporting of symptoms,” Koralnik explained.

Across all countries, the most common neurological complaints were brain fog, fatigue, muscle pain, headache, dizziness, and sensory disturbances (numbness, tingling). Nearly 60% of non-hospitalized patients in the U.S. reported insomnia, compared with roughly one-third or fewer in Colombia, Nigeria, and India. Statistical analysis also showed a clear divide between higher- and middle-income countries (U.S., Colombia) and lower-income countries (Nigeria, India).

The authors emphasize that long COVID affects millions worldwide, often young and middle-aged adults, reducing quality of life and work capacity. It is estimated that 10–30% of people who have had COVID-19 develop long-term symptoms.

The researchers conclude that these findings highlight the need for culturally sensitive diagnostic tools and healthcare systems capable of providing long-term monitoring and rehabilitation.