They estimated that 10 per cent of the 651 million documented Covid-19 cases around the world – at least 65 million people – have long Covid.
They quoted other studies suggesting that 10 to 30 per cent of non-hospitalised coronavirus cases would develop long Covid. The percentage increased to 50 to 70 per cent for hospitalised cases.
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However, the study did not clarify the definition of long Covid, and some of the findings contradicted those of previous studies.
According to the World Health Organization, PCC is defined as the continuation or development of symptoms that are present three months after a Sars-CoV-2 infection, with symptoms lasting for at least two months that cannot be explained through any other diagnosis.
Common symptoms include fatigue, shortness of breath, and cognitive dysfunction, which may fluctuate or relapse over time.
In an earlier study that examined data from 1.2 million patients from 22 countries who had Covid-19 in 2020 and 2021, an estimated 6.2 per cent experienced at least one of the three common long Covid symptoms three months after they were infected.
About 43 per cent of patients who were admitted to intensive care units developed long Covid, compared to 27.5 per cent of those who were admitted to general hospital wards, and 5.7 per cent of those who were not hospitalised.
The study was published in the Journal of the American Medical Association (JAMA) in October 2022.
Theo Vos, an epidemiologist at the Institute for Health Metrics and Evaluation at the University of Washington in Seattle, who is a corresponding author of the JAMA study, said compared with his findings, the proportion of people with long Covid quoted in the new article was considerably higher, which may partly be a definitional issue since his team concentrated on the main symptom clusters.
“More likely is that most of the studies quoted just report symptoms after Covid infection, and do not take into account that many of the long Covid-related symptoms are commonly reported even without Covid infection,” Vos said.
He added that with the Omicron variant, the risk of long Covid is between one half and one third of what it was compared with earlier variants, and recent vaccinations helped to lower the risk.
The new article in Nature Reviews Microbiology also quoted a study that said that few people with long Covid symptoms fully recover within one year.
“One study finds that 85 per cent of patients who had symptoms two months after the initial infection reported symptoms one year after symptom onset,” the article said.
It added that though future prognoses were uncertain, conditions known as ME/CFS – a multisystem neuroimmune illness, and dysautonomia – a disorder of the autonomic nervous system, were generally lifelong.
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Vos said the recovery time of long Covid quoted in the new study was contrary to his analysis, which indicated that by one year 85 per cent of people would have recovered.
“This sort of selective reporting on long Covid with exaggerated estimates does not help,” he said. “It is making quite a lot of policymakers sceptical, while long Covid is a serious condition affecting many individuals who are in need of supportive care as long as there are no clear treatments.”
To ensure an adequate response to the long Covid crisis, the authors said more comprehensive research, public communication campaigns, and policies and funding support were needed.
“We need research that builds on existing knowledge and is inclusive of the patient experience, training and education for the healthcare and research workforce,” the authors said.
