Researchers have found that people with longer-term Covid-19 symptoms including brain fog showed reduced performance in tasks testing different mental processes up to two years after infection with the virus.

Researchers from King’s College London looked at whether infection with Covid-19 affected performance of over 3,000 participants in two rounds of online cognitive testing on memory, attention, reasoning, processing speed and motor control that took place in 2021 and 2022.

The results, published in the journal eClinicalMedicine, showed those who had experienced symptoms related to the virus for 12 weeks or more had the worst scores.

In these people, the effect of Covid-19 on test accuracy was comparable in size to the effect of a 10-year increase in age.

There was no significant improvement in these test scores between the two rounds of testing, which took place nine months apart.

By the second round of testing, the average time since participants’ initial Covid-19 infection was almost two years.

On the other hand, people who felt fully recovered after Covid infection performed similarly to those who had not had the virus at all.

“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,” said lead author Nathan Cheetham, a Senior Postdoctoral Data Scientist at King’s College London.

“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,” he added.

Prof. Claire Steves, a Professor of Ageing and Health at King’s College London, said they used sensitive tests to measure speed and accuracy across a range of brain challenges.

The results show that some individuals have measurable changes in these tests after Covid going on for nearly two years.

“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. We need more work to understand why this is the case and what can be done to help,” Steves said.