• The term "long Covid" refers to patients suffering from prolonged illness after initially contracting the virus, with symptoms including shortness of breath, migraines and chronic fatigue.
• A preliminary study published Tuesday on MedRxiv is thought to represent the largest collection of symptoms identified in the long Covid population to date.
• The most frequent symptoms experienced after a period of six months were fatigue, post-exercise tiredness and cognitive dysfunction.

LONDON — The largest global study of "long Covid" to date has found that many of those suffering from ongoing illness after infection with Covid-19 are unable to return to work at full capacity six months later.

The term "long Covid" refers to patients suffering from prolonged illness after initially contracting the virus, with symptoms including shortness of breath, migraines and chronic fatigue.

Public discourse on the pandemic has largely tended to focus on those with a severe or fatal illness, with ongoing medical problems either underappreciated or misunderstood. However, recent studies have shown a growing number of Covid patients experience persistent symptoms, with some patients referring to themselves as "long haulers."

A preliminary study published Tuesday on MedRxiv is thought to represent the largest collection of symptoms identified in the long Covid population to date.

In the study, which was not peer-reviewed, the researchers surveyed 3,762 people ages 18 to 80 from 56 countries to identify the symptoms and other issues stemming from long Covid.

It recorded 205 symptoms in 10 organ systems, with 66 symptoms traced over seven months. On average, respondents experienced symptoms from nine organ systems.

What were the findings of the study?

The most frequent symptoms experienced after six months were: fatigue, tiredness after exercise and cognitive dysfunction, sometimes referred to as brain fog.

Respondents with symptoms over six months experienced an average of 13.8 symptoms in month seven, according to the study by members of Patient Led Research for COVID-19, a self-organized group of long Covid patients who are also researchers.

Over 45% of respondents reported requiring a reduced work schedule compared with pre-illness and 22.3% said they were not working at the time of the survey due to their health condition. Almost 86% experienced relapses, with exercise, physical or mental activity and stress identified as the main triggers.

The analysis was limited to suspected and confirmed Covid cases with illness lasting over 28 days and onset prior to June. This was to allow for an examination of symptoms over an average duration of six months, researchers said.

"We mustn't forget Long Covid," Dr. Gabriel Scally, president of epidemiology at the Royal Society of Medicine, said via Twitter on Tuesday.

"Thousands of new cases are developing every day. Vaccination is vital but it must be done effectively and backed up by other control measures that Independent Sage has tirelessly advocated," said Scally a member of the scientific group that provides scientific advice about the pandemic to the U.K. government and public.

The results of the study come as countries across Europe impose strict new health measures in an effort to curb the spread of the coronavirus.

More than 85 million people worldwide have contracted Covid, with 1.85 million deaths, according to data compiled by Johns Hopkins University.