Study criticises research: Risk of Long Covid may be overestimated

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Positive Corona rapid test: An illness can have long-term consequences

Photo: Sebastian Gollnow / dpa

Tiredness, exhaustion, difficulty concentrating: Some symptoms of a corona infection do not disappear with the negative test result. They can remain or recur weeks to months after infection and significantly restrict the everyday life of those affected. However, the risk of actually contracting Long Covid may be overestimated. This is suggested by a study by researchers from the USA. Accordingly, many scientific publications on the incidence of the disease had blatant methodological deficiencies. The problem is exacerbated by the inclusion of poorly conducted studies in reviews and meta-analyses, they say. The authors warn that this could unnecessarily stir up concerns among the population.

The results were published in the British Medical Journal. They are to be understood as a scientific opinion piece. A detailed study is not the basis of the work. Uninvolved scientists, however, consider the criticism to be appropriate.

Among the authors of the current publication is Tracy Beth Høeg from the University of California in San Francisco. She and her colleagues criticize, for example, the lack of or unsuitable control groups in studies on the frequency of Long Covid. With control groups, scientists check whether a circumstance actually has an effect and how much of it is practically a placebo. The team sees another problem in the broad definition of the disease.

Distortions at the beginning of the pandemic

Currently, various long-term health consequences are summarized under the term "Long Covid". According to previous findings, there is no uniform clinical picture, but various ones that can occur after a previous Sars-CoV-2 infection. Høeg's group is therefore in favour of stricter criteria: one should include persistent symptoms after a confirmed corona infection and take into account initial characteristics such as physical and mental health. The researchers also criticise the fact that the Long Covid definitions of international health bodies do not require a causal relationship between infection and long-lasting symptoms. "In general, inaccurate definitions in the scientific literature have led to more than 200 symptoms being associated with the condition referred to as long COVID," the study said.

In view of the broad definition, researchers have an obligation to compare the type and frequency of reported symptoms in infected people with cases in non-infected people – ideally in terms of demographics or underlying health, for example, it adds. However, this has often not happened, as a systematic review at the end of last year showed. According to the evaluation, only 22 out of 194 studies on Long Covid had control groups.

Distortions would have occurred especially in the initial phase of the pandemic, when corona tests were not yet widespread, the authors of the current publication write. Since fewer people with no or mild symptoms were included in the investigations, it was more likely that studies contained a non-representative sample of patients who tested positive. This makes it difficult to generalize the results, the researchers write. In the study, the team itself summarizes all symptoms that occur as a direct consequence of a corona infection and last at least twelve weeks under Long Covid.

"We have to take this disease seriously"

Some scientists who were not involved in the publication share the views of the study authors. Clara Lehmann from the University Hospital of Cologne, for example, agrees with the described deficiencies in research and also fears a distorted risk of disease. However, she also emphasizes to the Science Media Center (SMC): "Long or Post Covid is not a pipe dream." In some patients, blatant inflammatory reactions could still be detected several weeks after infection. "We need to take this disease seriously, but it requires an honest scientific determination of the actual risk of disease," she said.

"The number of apparent Long Covid patients is enormous," Peter Berlit of the German Society of Neurology told SMC. "The practices are overflowing, especially those of family doctors, pulmonologists and neurologists." Therefore, it is important to narrow down the term. "If several million euros are now made available for research, we should be sure that they will go to the right places."

According to Christa Scheidt-Nave of the Robert Koch Institute, assessments of the frequency of Long Covid often give the impression that it is a uniform, well-defined clinical picture. However, this is not the case. "Rather, the clinical presentation is variable and, according to current knowledge, is very strongly influenced by gender, age, course of the acute infection and pre-existing diseases or disease risks."

There is also criticism of the current publication. "Unfortunately, this is a flawed analysis that creates more misconceptions about Long Covid than it eliminates," Jeremy Rossman of the University of Kent told the UK's SMC. The authors had only referred to a limited number of studies and "applied them across the board and inappropriately to all Long Covid research." In order to draw general conclusions about an area of research, a thorough examination of the literature is required," says Rossman.

Ani