A new study published in the Lancet looked at the effects of COVID-19 on cognitive performance in a community-based cohort.
“Many people report ongoing symptoms after COVID-19, including brain fog and problems with concentration, memory and attention,” study author Dr. Rose Penfold told us. “Previous research has shown that some of these people perform worse on cognitive testing. However, most of this research has been done in hospitalized patients who had more severe infection.”
Dr. Rose Penfold is a clinical academic and one of the lead authors on the project. She is a Visiting Research Fellow at the Department of Twin Research and Genetic Epidemiology at King’s College London and a Multimorbidity PhD Fellow at the University of Edinburgh.
Before this study, little was known about whether people living in the community, most of whom were not hospitalized and did not seek medical attention, also experience cognitive impairment, and to what extent. It was also unclear whether symptoms and observed deficits improved over time.
“We wanted to find out whether previous COVID-19 infection is associated with cognitive performance in people living in the community,” Penfold told us. “We wanted to know whether any relationships that we found might be affected by the duration of symptoms and by ongoing symptoms at the time of testing. By asking participants to complete the tests at two time points, we also wanted to look at whether there was any improvement over time.”
Based on the researchers’ review of existing evidence, they thought that individuals who had experienced a longer duration of COVID-19 symptoms (long COVID) might show larger deficits in their cognitive performance. They also thought that individuals with ongoing symptoms might show larger deficits than people who felt fully recovered at the time of testing.
“It is over three years since the World Health Organization declared COVID-19 to be a global pandemic, and the majority of people infected recover within a few weeks,” Penfold told us. “However, at least 65 million people are estimated to struggle with long COVID, a debilitating condition, and many of these people experience fatigue and cognitive symptoms such as brain fog which impair their ability to work and do normal day to day activities.”
Most of these people live in the community and did not seek medical attention at the time of their initial infection. There is an unmet and pressing need to understand whether and how COVID-19 affects cognition in these people, who is affected and how long any effects may last. This is important to understand why some people continue to be affected by COVID-19 long after initial infection and what can be done to help.
“We invited over 8000 volunteer participants from the COVID Symptom Study Biobank to this study and over 3000 people took part,” Penfold told us. “Participants were grouped based on whether they had had COVID-19, and also by the duration of their symptoms.”
Participants were invited to two rounds of testing nine months apart. For each round, participants completed a set of 12 cognitive tasks using the « Cognitron » online platform. Researchers looked at both their accuracy and speed in each task and also combined scores across the tasks to calculate an overall score. At the same time as doing the cognitive tasks, participants completed short questionnaires asking about mood, tiredness and any effects of symptoms on their daily life.
Researchers used data from a previous questionnaire to assess whether participants felt they had fully recovered from COVID-19.
“We put all of this information together to look at whether there was a difference in task accuracy and speed in people who had had COVID-19, and whether performance was affected by the duration of symptoms and by any ongoing symptoms,” Penfold told us. “We took into account other factors in our analyses which are known to affect task performance, including age, physical and mental health conditions and educational attainment. We also compared scores between the two tests to look at whether there was any change over time.”
The researchers found some differences in task accuracy between individuals with previous COVID-19 infection when compared to individuals who had not been infected. However, these were only seen in people who did not feel fully recovered and back to normal at the time of testing.
Individuals who had been infected but felt fully recovered performed similarly to those who had not had COVID-19 at all. Differences were most marked in those who had experienced symptoms lasting longer than 12 weeks (long COVID). The changes in task accuracy that were observed in these people were similar to the changes seen when people are hospitalized during an illness and are comparable in size to the effect of a ten-year increase in age.
For people who had cognitive deficits detected in the first round of testing, there was no significant improvement in the second round of testing which took place nearly two years after their initial COVID-19 infection.
“Our findings partly supported our prior theory – that individuals with ongoing symptoms showed bigger deficits than those who felt fully recovered and these deficits were greatest in those who experienced a longer duration of symptoms,” Penfold told us. “It was reassuring to see that COVID-19 did not seem to affect performance for those who felt fully recovered.”
However, researchers were concerned to see that nearly two years following the first infection, some people still don’t feel fully recovered and that they continue to be impacted by the longer-term effects of COVID-19 with no improvement in test accuracy scores.
“Millions of people worldwide continue to experience ongoing symptoms related to COVID-19,” Penfold told us. “The cognitive deficits that we observed may affect quality of life and day to day functioning for individuals and have wider societal impacts due to a reduced capacity to work and need for support. We need to provide support for the people who continue to be affected and to carefully monitor their recovery. More work is needed to understand why some individuals are still affected at nearly two years following their first infection and most importantly, what can be done to help.”