Since the pandemic, people have been reporting impaired cognitive ability months after being infected with COVID-19. These claims have been made by individuals, but have also been confirmed with objective testing. According to two studies, cognitive deficits increased with the severity of the illness during the initial infection, and people who needed respiratory support or mechanical ventilation experienced a deficit similar to someone aging 20 years, from 50 to 70 years old. In another study performed in the UK, cognitive testing before and after infection showed structural changes in patients’ brains.
However, much of the existing research into long COVID has used relatively small hospital cohorts, and has been limited to much shorter-term follow-up assessments. Moreover, none of these studies have tested both COVID-positive cases and a negative control group, or whether recovery from long-COVID also leads to improved cognitive performance.
The new study sought to address this. The researchers examined whether COVID-19 impacted participants’ cognitive performances (their working memory, attention, reasoning, and motor control) during two rounds of online cognitive testing that took place in 2021 and 2022. Over 3,000 participants were recruited from the COVID Symptom Study smartphone app, which launched in the UK in March 2020. All the information was collected with informed consent.
The participants whose test scores were the most impacted were those who had had COVID-19 symptoms for 12 or more weeks. These individuals showed signs of cognitive impairment that were equal to 10 years of aging.
These participants did not score significantly higher during the second round of testing, which took place nine months after the first test. By the second round of testing, it has been almost two years since most of the participants had initially been infected with COVID-19.
However, the researchers found that participants who felt fully recovered from their COVID-19 infection performed similarly to those who had not had the virus.
“Our findings suggest that, for people who were living with long-term symptoms after having COVID-19, the effects of the coronavirus on mental processes such as the ability to recall words and shapes are still detectable at an average of almost two years since their initial infection,” lead author Dr Nathan Cheetham, a Senior Postdoctoral Data Scientist at King’s College London said in a statement.
“However, the result that COVID had no effect on performance in our tests for people who felt fully recovered, even if they’d had symptoms for several months and could be considered as experiencing ‘long COVID’, was good news. This study shows the need to monitor those people whose brain function is most affected by COVID-19, to see how their cognitive symptoms continue to develop and provide support towards recovery.”
According to study author Professor Claire Steves, a Professor of Ageing and Health at King’s College London, the study’s results show that more needs to be done to explore the impacts COVID has had on certain people.
“The fact remains that two years on from their first infection, some people don’t feel fully recovered and their lives continue to be impacted by the long-term effects of the coronavirus," Steves said. "We need more work to understand why this is the case and what can be done to help.”
The study is published in eClinicalMedicine.