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Long COVID may decrease IQ by up to nine points


I have previously discussed the neurological complications from long COVID-19, and a new study has quantified the level of cognitive loss by measuring the differences in IQ between individuals who recovered quickly from COVID-19 and those who had long COVID.

Although we are about to enter the fifth year of this pandemic, we still don’t fully appreciate the long-term effects of this disease. This new study helps us understand the neurological deficit that long COVID-19 may cause.

This article will review this new research and try to explain its findings.

What is long COVID-19?

Post-acute sequelae of SARS-CoV-2 infection (also called long-haul COVID or simply, long COVID) are conditions, including, but not limited to, neuropsychiatric, digestive, pulmonary, cardiovascular, and diabetes. These conditions persist long after the SARS-CoV-2 infection has passed. There is no test to diagnose long COVID conditions, and some individuals may have a wide variety of symptoms that could result from prior health conditions but are exacerbated by COVID. This can make it difficult for healthcare providers to recognize post-COVID conditions. 

Worse yet, since the symptoms are so difficult to explain, they are often very difficult to manage. There is no known “cure” for long COVID, so healthcare professionals have to focus on treating the symptoms, not a favorite technique of most science-based physicians.

Some people love to point out that the vast majority of people survive a COVID-19 infection (while ignoring the large number, over 1 million in the USA alone, that have died). However, they fail to consider long-COVID, which may have more serious complications than the initial COVID-19 infection itself.

By September 2023, the CDC estimated that 7% of all American adults had experienced long COVID at some point.

Let me make this point again — COVID-19 vaccines reduce the risk of serious disease complications including developing long COVID-19.

Long COVID and IQ paper

In a paper published on 29 February 2024 in the highly respected New England Journal of Medicine, Professor Adam Hampshire, Ph.D., School of Public Health, Imperial College London, London, UK, and colleagues designed several online tasks to measure participants’ cognitive function. More than 140,000 people completed at least one of the tasks, while almost 113,000 finished all eight.

As there is no scientific consensus around the definition of long covid, the study instead looked at symptom duration, comparing the results of people who had not had COVID-19 to those who were infected but recovered in less than four weeks, those who recovered between four and 12 weeks and those whose symptoms continued after that. They used a measure of IQ to determine possible cognitive changes after long COVID-19.

Here are the key results from the study:

  • Participants who recovered from covid symptoms had a cognitive deficit equivalent to three IQ points compared with those who were never infected,
  • Participants suffering from unresolved covid symptoms lasting 12 weeks or more experienced a loss equivalent to six IQ points.
  • Researchers also stressed that the greater cognitive decline associated with persistent symptoms may not be permanent, as the length of the study was limited.
  • The effect was greater among participants who were infected earlier in the pandemic.
  • Participants who were admitted to the intensive care unit had the largest loss of IQ, around nine points compared to people who did not contract COVID-19.
  • Among those who contracted COVID-19, the researchers found “a small cognitive advantage among participants who received two or more vaccinations.” More evidence that vaccines have a long-term benefit to those who contract COVID.

Summary of long COVID and IQ research

In an accompanying editorial, the authors wrote:

The results of the study by Hampshire and colleagues are of concern, and the broader implications require evaluation. For example, what are the functional implications of a 3-point loss in IQ? Whether one group of persons is affected more severely than others is not clear. Whether these cognitive deficits persist or resolve along with predictors and trajectory of recovery should be investigated. Will Covid-19–associated cognitive deficits confer a predisposition to a higher risk of Alzheimer’s disease or other forms of dementia later in life? The effects on educational attainment, work performance, accidental injury, and other activities that require intact cognitive abilities should also be evaluated. SARS-CoV-2 infection happened in the context of a global pandemic that disrupted many facets of our lives; disentangling the effects of the infection from those of the pandemic (e.g., social isolation, grief, and trauma) should also be undertaken.

The editorial points out one of the important weaknesses of the study — the cognitive decline was measured between groups. Still, it did not determine if there was a decline in individuals, as the researchers did not have an IQ measurement prior to COVID-19 or long COVID.

However, as the editorial states, these results are concerning. Even though the IQ deficit appears to be small, that’s an average — there are individuals, especially those who had to go to the ICU for treatment, with much larger IQ deficits. This could lead to a significant burden on society if the cognitive deficits are permanent.

I think we are just scratching the surface of the long-term effects of long COVID.

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Michael Simpson

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