A little over three years since the start of the COVID-19 pandemic, we still have much to learn about the SARS-CoV-2 virus’ lingering effects once the initial infection has subsided, but research over the last several years has yielded many valuable insights. In one recent study, Swiss researchers discovered that a person’s risk of developing Long COVID symptoms may be significantly less if their first infection has been recent.*

Lingering effects of COVID-19 variants unclear

How different COVID-19 variants, like Omicron, affect Long COVID development remains an important research question, as previous European studies have shown mixed results.

• In a U.K. study published in The Lancet, health data of 97,000 people showed that those infected with the Omicron variant had a roughly 50% less chance of reporting symptoms lasting a month or longer after infection than people who had the Delta variant. 
• On the other hand, a Norwegian study of 57,000 people, published in the journal Nature, showed that those infected with both Delta and Omicron variants had an equal chance of reporting Long COVID symptoms (fatigue, cough, breathlessness, rapid heartbeat, and anxiety or depression) as much as four months later.

What the researchers did

For the Swiss study, researchers Carol Strahm, M.D. and Philipp Kohler, M.D., M.Sc. at Switzerland’s Cantonal Hospital St. Gallen followed a group of 1,200 Swiss healthcare workers, composed mostly of female nurses.

• Participants underwent regular PCR testing from February 2020-January 2021, when the original COVID virus dominated, and from January-June 2022 during Omicron.
• Participants were assessed for Long COVID symptoms (fatigue, lack of smell or taste, and breathlessness) via online questionnaires in March and September 2021, and then again in June 2022.

What they found

Results of the Swiss study were similar to those of the U.K. study.

• Participants infected with the Omicron variant had no greater likelihood of Long COVID than people who never had COVID-19.
• Comparatively, people infected with the original virus had as much as a 67% greater chance of Long COVID than those who never had COVID-19.

Results again resembled the U.K. study in people infected with the original virus versus Omicron.

• Long COVID symptoms were no more likely after Omicron than after the original COVID infection.

By the third questionnaire, some people with the original virus still had Long COVID symptoms, while most whose first infection was with Omicron did not.

• Vaccination (booster shot) status had no apparent effect on Long COVID development.

The study findings have yet to be published but will be presented at the 2023 European Congress of Clinical Microbiology and Infectious Diseases.

What it means

“The wild-type [original] virus is by far the strongest risk factor for Long COVID-19,” Kohler said. Omicron has been shown to cause milder infections in healthy people, and Long COVID is more likely after severe illness.

He explained that differing study results could be due to varying definitions of Long COVID and study populations. While their own study is limited by a smaller sample size, and only involved healthcare workers, who were closely monitored. Still, he said, “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.”

Kohler and Strahm intend to administer a fourth Long COVID questionnaire to see whether these post-viral differences between the original strains and Omicron variants remain.

*Park, A. (2023, March 8). People Are Far Less Likely to Get Long COVID After Omicron, Study Finds. Time Magazine. https://time.com/6261074/long-covid-omicron-less-likely