A Northwestern Medicine-led study of more than 3,100 adults with long COVID found that non-hospitalized participants in the United States reported substantially higher rates of brain fog, depression/anxiety and insomnia than participants in Colombia, Nigeria and India—differences the researchers say likely reflect cultural factors and access to care as much as biology.
A Northwestern Medicine-led international study has found sharp cross-country differences in how adults with long COVID report cognitive and psychological symptoms.
The study, published Jan. 28, 2026 in Frontiers in Human Neuroscience, analyzed data from more than 3,100 adults with persistent neurological symptoms after SARS‑CoV‑2 infection. Participants were evaluated through university-affiliated medical centers and research sites in Chicago; Medellín, Colombia; Lagos, Nigeria; and Jaipur, India.
Among patients who were not hospitalized during their initial COVID-19 infections, 86% of participants in the United States reported “brain fog,” compared with 63% in Nigeria, 62% in Colombia and 15% in India. Measures of psychological distress followed a similar pattern: nearly 75% of non-hospitalized U.S. participants reported symptoms consistent with depression or anxiety, compared with about 40% in Colombia and fewer than 20% in Nigeria and India. Sleep symptoms also differed; nearly 60% of non-hospitalized U.S. participants reported insomnia, versus roughly one-third or fewer in the other locations.
Across the sites, frequently reported neurological symptoms included brain fog, fatigue, myalgia (muscle pain), headache, dizziness and sensory disturbances such as numbness or tingling.
The researchers cautioned that higher reported symptom rates in the U.S. do not necessarily mean the virus is causing more severe disease there. Instead, they said differences in stigma, cultural norms around discussing mental health and cognitive problems, and access to neurological and mental health care may influence whether people disclose symptoms and seek evaluation.
“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, the study’s senior author and chief of neuro-infectious disease and global neurology at Northwestern University Feinberg School of Medicine. He added that stigma, misperceptions, religiosity and belief systems, limited health literacy, and shortages of mental health providers may contribute to underreporting in some settings.
In statistical analyses, symptom patterns aligned more closely with national income classifications than geography, with higher reported burdens in higher-income settings such as the United States and Colombia compared with lower-middle-income settings such as Nigeria and India.
The authors described the results as another signal of long COVID’s broad social and economic consequences, particularly when symptoms affect working-age adults. They also called for culturally sensitive screening approaches that can better detect cognitive and mood symptoms in different settings.
Building on the findings, the team said it is testing cognitive rehabilitation approaches for long COVID-related brain fog in Colombia and Nigeria using a protocol developed at Northwestern’s Neuro-COVID-19 clinic in Chicago.
