But the research also revealed that a similar cohort who were recovering from the flu showed 43 per cent of people also had one or more of the same symptoms recorded during the same time period.
This has led some to suggest the existence of ‘long flu’, and to wonder whether there are patients who have been silently suffering from the illness all along. We spoke to the researchers behind the new paper to find out.
“It might well be – and the emphasis is on the might – that there is such a thing as long flu that’s been ignored simply because it hasn’t received as much attention as we are now giving to COVID,” said Dr Max Taquet, from the department of psychiatry at University of Oxford and first author of the new study.
“But the data that we have, and the data that many other people have shown in the past, is that if there is such a thing as long flu, it seems to be less common than long COVID.”
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The team report that COVID-19 patients were 1.5 times more likely to report a long COVID symptom than those who’d had the flu.
This was the case for all nine symptoms that the researchers investigated, the most common of which were breathing problems, abdominal symptoms, fatigue, pain and anxiety/depression. They also analysed patients’ data for reports of chest or throat pain, cognitive problems (also called ‘brain fog’), headache and muscle pain.
For these symptoms to be considered as long COVID, or post-illness, they must occur at least three months after the COVID-19 infection. In the COVID cohort, 37 per cent of patients had at least one symptom diagnosed in the three-to-six month period.
For those recovering from flu, 29 per cent had at least one symptom three to six months later. But Taquet warns that this doesn’t show that there’s such a thing as long flu – to do so, they’d need to compare the data with a similar cohort, a control group, from the general population who haven’t had the flu or COVID-19.
“However, 30 per cent seems quite a high number, so it would be very surprising if those symptoms were [as prevalent] in the general population,” he said.
“We can’t say for sure that this is not the case. I guess the findings strongly suggest that there might be such a thing as long flu, or at least, to be a little bit more cautious, that there are some people who still experience symptoms in the three to six months after after the flu.”
But does this mean having long flu, if it can be called that, is as bad or worse than long COVID?
“We didn’t just measure individual symptoms, but also how likely it was that two or more would occur together,” explained Prof Paul Harrison, a professor of psychiatry at University of Oxford who also worked on the new research.
“With COVID, people were much more likely to get pairs or groups of symptoms than after flu. Roughly 50 per cent more likely for each of the nine symptoms.”
Harrison says it’s easy to move the focus too much onto the flu. “Perhaps the public are a bit tired of hearing about long COVID, and the mention of long flu was what was most novel to the media.”
The team, Harrison says, compared COVID to flu to give context. “We wanted to see if the symptoms were just about recovering from any viral illness, not just COVID itself.
“We actually decided not to call it ‘long influenza’ in our paper,” he said. “[In medicine] we do talk about post-viral fatigue… people do attribute long term illnesses with a specific event, such as those who get chronic Lyme disease or ME.”
These patients may have felt let-down by clinicians, Harrison admitted, as medicine has not known how to help them. Research into long COVID could change that.
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But why not go further, and ask if instead we should call all post-viral illnesses ‘long virus’?
“That would generalise even further and I think we need to be cautious about that,” said Taquet.
“We don’t know that all viruses cause it. We don’t even know whether it’s only viruses – it could be all infections, including bacterial infections.
“But perhaps COVID has created that window of opportunity to focus on how long it takes to completely recover from an infection. Now that we have the resources, we know how to do it, we can start looking into the same things for other infections. But I wouldn’t go as far as saying that there’s such a thing as long virus. I do not think it’s a possibility, but I do not know that that’s the case.”
So, is long COVID still a useful phrase, or should it be scrapped for being too ambiguous?
Taquet says it’s still a useful concept for patients and clinicians.
“Patients came up with it, which is quite new in the field of medicine, and they came up with it because they thought it was helpful. And I think that is important to recognise. There’s nothing more frustrating than for a patient who is suffering with quite a lot of debilitating symptoms to just be told ‘Well, it’s nothing’ or even worse, ‘it’s all in your mind’.
“I don’t think we should scrap it, but I think we do need we definitely need a lot more research into trying to understand what it is, whether it is one long COVID, or many long COVIDs, which is another question and certainly what are the mechanisms and how to treat them.”
About our experts
Dr Max Taquet is the NIHR academic clinical fellow in psychiatry at University of Oxford. He works within the Precision Psychiatry lab, which aims to improve the current treatment practice in the NHS and across the world.
Professor Paul Harrison is a professor of psychiatry at University of Oxford. During the pandemic he has been actively involved in research into the psychiatric and neuropsychiatric effects of COVID-19.