Brain fog associated with long Covid is comparable to ageing 10 years, researchers have suggested.

A study by King’s College London explored the impact of long Covid on thinking and memory skills for a paper published in eClinicalMedicine.

The team studied people included in the Covid Symptom Study Biobank who were recruited via the Covid Symptom Study smartphone app.

Those in the study included people with Covid and varying degrees of symptoms and people without the illness.

They were given 12 tasks testing memory, attention, reasoning, processing speed and motor control.

Researchers said the impact of Covid on test accuracy “was comparable in size to the effect of a 10-year increase in age” and scores were most affected in people who had symptoms of the virus for 12 weeks or more.

The study was split into two rounds nine months apart.

Some 3,335 people completed the first round, which took place in July and August 2021, with 1,768 going on to complete the second round between April and June 2022.

Researchers found no significant improvement in scores between two rounds.

By the time the second round was conducted, the average time since participants’ initial infection was almost 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

Lead author Dr Nathan Cheetham, a senior postdoctoral data scientist at King’s College London, said: “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.”

People who said they felt fully recovered from Covid – even if they had symptoms for several months – performed similarly to those who had not had the virus at all.

Dr Cheetham hailed this element of the study as “good news”.

Claire Steves, a professor of ageing and health at King’s College London, said: “We used sensitive tests to measure speed and accuracy across a range of brain challenges.

“This study shows that some individuals have measurable changes in these tests after Covid-19 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.”