The risks of developing long Covid have been “distorted” by flawed research, leading to heightened public anxiety, academics have claimed.
They suggest “major flaws” in the body of literature on the condition have likely exaggerated the true threat of developing it.
Most people who contract Covid-19 feel better within days or weeks, but for some people symptoms can last longer than 12 weeks.
Those who have long Covid, also known as post-acute sequelae of Covid-19 (PASC), report fatigue, brain fog, chest pain and shortness of breath.
However, analysis from researchers in the UK, Denmark and the USA said “many scientific publications” overestimate the prevalence of long Covid due to “overly broad definitions, lack of control groups, inappropriate control groups, and other methodological flaws”.
They argue the symptoms are common among many upper respiratory viruses.
The team warned that a lack of definition could could lead to increased healthcare spending and more anxiety among the public, as well as misdiagnoses and a diversion of funds away from patients who have other long-term conditions.
The paper, published in BMJ Evidence Based Medicine, looked at the definition of long Covid by a number of global health organisations, including the National Institute for Health and Care Excellence (Nice) and the World Health Organisation (WHO).
They claim “none of them requires a causal link” between Covid-19 infection, meaning any new symptoms that happen after a confirmed or suspected infection could be considered consistent with long Covid.
“In general, in the scientific literature, imprecise definitions have resulted in more than 200 symptoms being associated with the condition termed long Covid,” they said.
The team also point out that studies in the early stages of the pandemic are likely to have included fewer patients with mild or no symptoms.
This could lead to sampling bias, they said, which occurs when certain groups are more likely to be included in a study than others, limiting the findings.
Researchers added: “Our analysis indicates that, in addition to including appropriately matched controls, there is a need for better case definitions and more stringent (long Covid) criteria, which should include continuous symptoms after confirmed SARS-CoV-2 infection and take into consideration baseline characteristics, including physical and mental health, which may contribute to an individual’s post Covid experience.”
In future, research should included properly matched control groups, the paper said, as well as “sufficient” follow-up time after infection.
They also called for “internationally established” diagnostic criteria and called for studies to avoid the “umbrella term” and instead “narrowly define” certain post-Covid symptoms.
“Ultimately, biomedicine must seek to aid all people who are suffering,” the team added. “In order to do so, the best scientific methods and analysis must be applied.
“Inappropriate definitions and flawed methods do not serve those whom medicine seeks to help.
“Improving standards of evidence generation is the ideal method to take long Covid seriously, improve outcomes, and avoid the risks of misdiagnosis and inappropriate treatment.”
Dr Adam Jacobs, senior director of biostatistical science at Premier Research, said: “It is, of course, inevitable that much of this literature is imperfect. Long Covid simply didn’t exist four years ago, so researchers have had to get to grips with a new and challenging topic at top speed.
“It is, therefore, not surprising that different studies have different estimates of the prevalence of long Covid, as studies have used different case definitions, different populations etc.”
He added that while the paper “makes some sensible points” it goes on “to draw some odd conclusions”.
Dr Jacobs cited a survey by the Office for National Statistics (ONS) on long Covid, which was discontinued in March. Prior to this, it counted 1.9 million people in the UK with long Covid, which he said is “staggeringly high”.
The number of people also “economically inactive” due to sickness is also at a record high, Dr Jacobs said.
“We don’t know how long those people will remain ill. If we are lucky, most of them will be healthy again within a year or two. If we are unlucky, a large number of them may have a permanent disability.
“And perhaps their numbers will be swelled still further as Covid continues to circulate in the population and people are repeatedly infected.
“Are we willing to just assume that we will be lucky in the face of such a catastrophic threat to population health? The precautionary principle requires that we take this threat very seriously indeed.”
“New research is appearing all the time, and we are constantly learning more about the prevalence of long Covid, the various forms it can take, and the mechanisms behind it.
“In fact, just last week another study was published showing that patients hospitalised with Covid were significantly more likely to have multi-organ abnormalities detected on MRI at a median of five months after hospital discharge, particularly in the lung, brain and kidneys. That does not strike me as “reassuring”.”
Dr Jacobs said more research into the condition is needed and if researchers can make studies “more methodologically robust then that will be a good thing”.