The research from the University of Oxford and the National Institute for Health Research (NIHR) Oxford Health Biomedical Research Centre (BRC) investigated long-COVID in over 270,000 people recovering from COVID-19 infection, using data from the US-based TriNetX electronic health record network.

The most common long-COVID symptoms were breathing problems, abdominal symptoms, fatigue, pain and anxiety/depression.

“The results confirm that a significant proportion of people, of all ages, can be affected by a range of symptoms and difficulties in the six months after COVID-19 infection,” said NIHR Academic Clinical Fellow Dr Max Taquet, who led the analysis at the University of Oxford.

“These data complement findings from self-report surveys, and show that clinicians are diagnosing patients with these symptoms. We need appropriately configured services to deal with the current and future clinical need,” said Taquet.

Higher rates were seen if the whole 1-180 day period after a COVID-19 infection was included.

Severity of infection, age, and sex affected the likelihood of long-COVID symptoms: long-COVID symptoms were more frequent in those who had been hospitalised, and they were slightly more common in women. These factors also influenced which of the symptoms people were most likely to experience.

For example, older people and men had more breathing difficulties and cognitive problems, whereas young people and women had more headaches, abdominal symptoms and anxiety/depression. Many patients had more than one long-COVID symptom, and symptoms tended to co-occur more as time progressed.

“Research of different kinds is urgently needed to understand why not everyone recovers rapidly and fully from COVID-19,” said Professor Paul Harrison, who headed the study, Department of Psychiatry, University of Oxford.

“We need to identify the mechanisms underlying the diverse symptoms that can affect survivors. This information will be essential if the long-term health consequences of COVID-19 are to be prevented or treated effectively,” he said.

The study also looked at the same symptoms in people recovering from influenza or flu. Long-COVID symptoms did occur after influenza, but were 1.5 times more common after COVID-19.

According to the findings, the nine core long-COVID symptoms, occurring 90-180 days after COVID-19 was diagnosed, comprise: Abnormal breathing (8%); abdominal symptoms (8%); anxiety/depression (15%); chest/throat pain (6%); cognitive problems or so-called brain fog (4%); fatigue (6%); headache (5%); myalgia or muscle pain (1.5%); other pain (7%); and any of the above features (37%).

The study highlights that it does not explain what causes long-COVID symptoms, nor how severe they are, nor how long they will last. The results do not take into account people who had COVID-19 but were not diagnosed, for example because they were asymptomatic and did not get tested, nor COVID-19 survivors with long-COVID symptoms that had not been recorded in their health records.