Researchers still have a lot to learn about Long COVID—when symptoms linger long after a COVID-19 infection is over—but new data suggest there may be some good news for people infected with the virus more recently.
In a study that will be presented at the European Congress of Clinical Microbiology and Infectious Diseases in April (and which has not yet been published), researchers report that people who tested positive for COVID-19 during Omicron waves were no more likely to report lingering symptoms after recovery than people who had never had COVID-19. By contrast, those who were infected with the original SARS-CoV-2 variant were up to 67% more likely to report lingering symptoms than those who did not have COVID-19.
Dr. Carol Strahm and Dr. Philipp Kohler, both from the division of infectious diseases and hospital epidemiology at Cantonal Hospital St. Gallen in Switzerland, led the study of 1,200 health care workers in the country. The participants, mostly female nurses, agreed to regular PCR testing for COVID-19 during periods when the original virus was circulating, from February 2020 to January 2021, and during the Omicron wave from January to June 2022. In March and September 2021 and in June 2022, all of the participants answered an online questionnaire about any lasting symptoms they might be experiencing, which could include fatigue, loss of smell or taste, and shortness of breath. The aggregate of these symptoms made up a rough measure of Long COVID.
The results were similar when the research team looked at people who tested positive during the Omicron wave after being positive with the original virus; these people did not report any more Long COVID-like symptoms than people who had been infected once with the original virus. “The wild-type [original] virus is by far the strongest risk factor for Long COVID-19,” says Kohler.
Over the 18 months from the first and last assessments, people infected with the original virus showed fewer Long COVID symptoms, but some had symptoms that remained, while those whose first positive test was during the Omicron wave did not, on the whole, report continued symptoms after their infection. When the researchers looked at symptom reports by people’s vaccination status, they saw that booster shots did not seem to make a difference in whether people developed Long COVID or not. “We don’t see that the booster adds much more benefit, at least in terms of Long COVID, in our population,” says Kohler.
The results add to growing data about how the different variants affect short- and long-term health. And the data aren’t completely straightforward. Similar to the current study, a previous study from the U.K. involving health records of 97,000 people found that those who were infected with Omicron variants were about half as likely to report continued symptoms four weeks or more after their infection as people who were infected with the Delta variant. But a Norwegian study involving 57,000 people who tested positive found that people infected with Omicron and Delta strains were equally likely to report continued symptoms of fatigue, cough, heart palpitations, shortness of breath, and anxiety or depression up to four months later.
The differing findings could be related to the populations studied and how they defined symptoms, says Kohler. In general, Omicron causes milder infections in relatively healthy people, and data show that more severe disease is more likely to lead to the lingering symptoms of Long COVID. He notes that the size of his study was relatively small compared to the others, although it had the advantage of repeated questionnaires to track volunteers’ symptoms.
“We have a selected population of health care workers, and a limitation with the small sample size,” he says. “Still, in my opinion, the data show there is clearly less Long COVID—probably not much higher than in the uninfected population—among people whose first infection was with Omicron.”
Figuring out how the different variants may affect lingering symptoms is a key question in Long COVID research. Kohler and Strahm plan to ask the volunteers to answer another questionnaire about their symptoms in April to determine if the differences between infections with original and Omicron strains remain.
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