Cognitive impairment occurs even after asymptomatic or mild Covid disease, as a study conducted at Imperial College London shows. Cognitive decline affects memory, verbal intelligence and spatial thinking in particular. Long Covid sufferers experience the greatest losses.

Whether it is demands for a review of the containment measures adopted during the pandemic or shouts of “Covid is over!” to people who still have to or choose to wear masks: It is hard to avoid the impression that Germany has now definitely entered a post-pandemic reality. Consequently, air hygiene measures are now also being scaled back. HEPA filters in educational establishments – if ever they did exist – are now mostly meeting one of the following fates:

  • Scrapping
  • Storage “until the next pandemic”
  • Lack of maintenance
  • Ban on use.

Where none of these apply, they are often simply being ignored. After all, children, teenagers and young adults are supposed to forget the difficult times they experienced during the pandemic. Air hygiene would only get in the way. Or would it?

Study reveals cognitive decline after Covid-19

SARS-CoV-2, the virus responsible for the pandemic, seems unconcerned: Wastewater monitoring by the Robert Koch Institute, Germany’s federal agency for disease control and prevention, showed an unprecedented peak in wastewater contamination with SARS-CoV-2 in December 2023. This went largely unnoticed, while Germans never ceased to be puzzled over the numbers of staff on sick leave. However, the virus still demands to be noticed, as even mild Covid leads to a decline in cognitive abilities, as shown in a study by a research team led by Adam Hampshire of the Medical Faculty at Imperial College London. Their article was published in the New England Journal of Medicine.

People with long-term impairments following a Covid infection in particular report concentration problems, word-finding difficulties and similar symptoms which suggest a decline in cognitive abilities, i.e. abilities related to a person’s intelligence. In their study, the researchers therefore collected data using the Cognitron battery, an intelligence test that measures verbal and non-verbal reasoning and planning as well as working memory. More than 140,000 people took part in the study and almost 113,000 completed all tasks.

Since the researchers were primarily interested in finding out whether cognitive impairments depend on the duration and severity of a Covid illness, the participants were assigned to the following groups:

  • Not infected with Covid
  • Infected with Covid, but asymptomatic
  • Infected, with symptoms that resolved after less than four weeks
  • Infected, with symptoms that resolved after four to twelve weeks
  • Infected, with symptoms that resolved after more than twelve weeks
  • Infected, with symptoms that remained unresolved after more than twelve weeks and were still present at the time of data collection (“Long Covid”).

Earlier variants caused more damage than later ones

The fact that the virus kept changing during data collection was taken into account by sorting participants into groups according to the variant prevailing at the time of infection:

  • Original virus: up to 30/11/2020
  • Alpha (B.1.1.7.): 01/12/2020 to 30/04/2021
  • Delta (B.1.617.2): 01/05/2021 to 15/12/2021
  • Omicron (B.1.1.529): 16/12/2021 to 31/03/2022, which marked the end of data collection.

Good news first: With the transition to the Delta and, later, the Omicron variant, cognitive decline decreased. While it was still 0.32 standard deviations (SD) for the original virus, it is only 0.16 SD with Omicron, i.e. half as much.

Results may be represented in points on the IQ scale

Standard deviations are, for instance, used in intelligence tests to represent results. Thus, the IQ scale is defined by a  mean of 100 and a standard deviation of 15. Hence, if you move 15 points to the left and 15 points to the right from the mean value, this defines the range of intelligence that is commonly referred to as “average”. Average intelligence therefore means an IQ of 85 and 115. Slightly more than 68% of the population attain an IQ between 85 and 115. Values below 85 count as below average, values above 115 as above average.

A loss of 0.32 SD with the original virus therefore means a decline in cognitive abilities corresponding to 4.8 IQ points. Accordingly, a decline of 2.4 IQ points is to be expected with Omicron.

Cognitive decline occurs with all degrees of severity

A decline in cognitive abilities can even be observed with asymptomatic infections (see Figure 1). A loss corresponding to around 2.6 IQ points can be expected here. With symptomatic infections, the decline is similar regardless of how long it takes for the symptoms to resolve: A decline of between 3.5 and 3.9 IQ points was observed in those groups. People affected by Long Covid face the greatest problem: The frequently reported issues with reasoning, word finding and memory correspond to a loss of around 6.3 IQ points.

Chart shows cognitive decline according to duration and severity of Covid-19
Figure 1: Cognitive decline according to duration and severity of Covid-19

Memory is one of the most severely affected cognitive abilities (see Figure 2). Although all people who have been infected with Covid are affected, Long Covid sufferers have to cope with the greatest losses regarding immediate and delayed memory.

Chart shows cognitive decline regarding immediate and delayed memory after Covid-19
Figure 2: Cognitive decline after Covid-19 – Immediate and delayed memory

The area of verbal intelligence is also affected (see Figure 3). While there are similar losses with asymptomatic infection and symptoms which have not persisted, Long Covid sufferers again show the greatest decline for both word definitions and verbal reasoning based on analogies.

Chart shows cognitive decline regarding verbal intelligence after Covid-19
Figure 3: Cognitive decline after Covid-19 – Verbal analogical reasoning and word definitions

Spatial planning is also impaired in all groups (see Figure 4). Again, Long Covid sufferers are those who have to live with the steepest declines, although all groups who have been infected with Covid are concerned.

Chart shows cognitive decline regarding spatial planning after Covid-19
Figure 4: Cognitive decline after Covid-19 – Spatial planning

Educational institutions must protect learners’ cognitive skills

What does this mean for education? Schools take pride in providing learners with the best possible support to match their cognitive abilities. This should include ensuring that those cognitive abilities are not knowingly jeopardised. It is therefore still important to avoid Covid infection wherever possible.

The city of Bradford has shown how this can be done: The use of HEPA filters reduced the number of Covid infections amongst pupils by more than 20 %. The number of lessons cancelled due to teachers on sick leave can be reduced in the much the same way. Air filters will also reduce the number of Long Covid cases amongst teaching staff. Thus, the quality of teaching can be maintained, as cognitive impairments will lead to changes in lesson organisation and classroom management, and will also increase stress in teachers.

Indoor air hygiene must become a normal fact of life if we wish to maintain the cognitive performance of the current and future workforce.

Hampshire, A., A. Azor, C. Atchison, W. Trender, P.J. Hellyer, V. Giunchiglia, M. Husain, G.S. Cooke, E. Cooper, A. Lound, C.A. Donnelly, M. Chadeau‑Hyam, H. Ward & P. Elliott (2024). Cognition and memory after Covid-19 in a large community sample. The New England Journal of Medicine, 390(9).