A key common deficit in people with long COVID might be generalised to cognitive slowing, according to research.

COVID-19 survivors may experience a wide range of chronic cognitive symptoms for months or years as part of post-COVID-19 conditions (PCC) or long COVID-19.

To date, there is no definitive objective cognitive marker for PCC. The study "identified pronounced cognitive slowing in patients with PCC, which distinguished them from age-matched healthy individuals who previously had symptomatic COVID-19 but did not manifest PCC", said researchers from the University of Oxford.

"This might be an important factor contributing to some of the cognitive impairments reported in patients with PCC," they added. To examine cognitive slowing, patients with PCC completed two short web-based cognitive tasks, Simple Reaction Time (SRT) and Number Vigilance Test (NVT).

About 270 patients diagnosed with PCC at two different clinics in the UK and Germany were compared to two control groups -- individuals who contracted COVID-19 before but did not experience PCC after recovery (No-PCC group) and uninfected individuals (No-COVID group).

The results, published in the journal eClincialMedicine, showed cognitive slowing was evident even on a 30-sec task measuring SRT, with patients with PCC responding to stimuli about 3 standard deviations slower than healthy controls.

About 54 per cent of patients with PCC's response speed was slower than 2 standard deviations from the control mean, indicating a high prevalence of cognitive slowing in PCC.

Comorbidities such as fatigue, depression, anxiety, sleep disturbance, and post-traumatic stress disorder did not account for the extent of cognitive slowing in patients with PCC.

Furthermore, cognitive slowing on the SRT was highly correlated with the poor performance of patients with PCC on the NVT measure of sustained attention.

There was not a significant correlation between the severity of mental health symptoms and chronic post-COVID cognitive deficit. "The present study reported a significant psychomotor slowing in individuals diagnosed with PCC," the authors said.

"This might be an important factor contributing to some of the cognitive impairments reported in patients with PCC."