Omicron Much Less Likely to Cause Long COVID, Study Finds

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March 10, 2023 – Health care workers infected with the COVID-19 Omicron variant were far less likely to experience significant long COVID symptoms than those who contracted the original SARS-CoV-2 virus, according to new research out of Switzerland.

The results, which will be presented at the European Congress of Clinical Microbiology & Infectious Diseases conference in April and have been peer reviewed, showed that those infected with the original, “wild-type” virus circulating in the early months of the pandemic still had persistent post-COVID symptoms 18 months later. At the same time, a reinfection with Omicron among this group did not appear to increase their long COVID risks.

“In a young and healthy population, the risk of long COVID after Omicron infection, independent of vaccination status, is very low,” Philipp Kohler, MD, with the Cantonal Hospital St Gallen and principal investigator of the study, says in an email. 

“These data suggest that the long COVID wave after Omicron infection will not be as devastating as has been feared by many.”

The latest findings build on previous research, including an article published in The Lancet, that showed the risk of long COVID was lower with Omicron compared with the Delta variant. Another study published in Nature Communications comparing the same variants also saw lower risks of long-term symptoms with Omicron 3 months after testing positive.

In the Swiss study, which has yet to be submitted to a medical journal for publication, Kohler and his colleagues tracked 1,201 health care workers from nine domestic health care networks. Their vaccination status was tracked and symptoms were compared with an uninfected control group.

“Adjusting for this ‘background noise’ is very important because it allows to disentangle the effect of long COVID from other conditions, which are common in the general population and which cause similar symptoms as long COVID, such as fatigue,” Kohler said.

Health care workers completed online questionnaires three times over the next 2 years to say if they were experiencing any long COVID symptoms as well as how bad their fatigue was. Eighteen symptoms were covered, with loss of smell or taste, tiredness and weakness, burnout and exhaustion, and hair loss the most common issue reported.

In the study, those who tested positive with the original virus had a 67% higher risk of developing long COVID symptoms when surveyed in March 2021 compared with the control group of participants who remained uninfected. While symptoms declined over time, they were still present 18 months later.

Meanwhile, the chances of developing long COVID among workers whose first infection was with Omicron did not appear to be greater than those who had never contracted COVID-19, researchers found. The participants’ rates of fatigue were also comparable between the infected and uninfected groups.

“We can only speculate as to why this was,” Carol Strahm, MD, an infectious disease specialist and one of the researchers involved in the study, said in a statement. He added that it could be due to Omicron being less likely to cause severe illness than the original virus, as well as immunity acquired through previous exposure, including asymptomatic infections that never resulted in the development of antibodies.

Kohler did note that their sample size was not very large and that the group  studied is not reflective of the broader general population. Older individuals, those with other health issues, and the unvaccinated may not have the same outcomes, he said.

Linda Geng, MD, co-director of the Post-Acute COVID-19 Syndrome Center at Stanford University, who was not involved in the Swiss study, said while there is research suggesting that long COVID risks may be lower following infections with Omicron compared with earlier variants, she is still seeing many new patients.

“In our Long COVID clinic, we still see plenty of cases of long COVID that developed after more recent infections,” Geng, who is also a clinical assistant professor of medicine with the university’s Primary Care and Population Health, says in an email.

“We also don't know what the future will hold in terms of the evolution of the virus and its impact on long COVID risk. The only guarantee against long COVID is to not get COVID.” 

Going forward, the Swiss team plans to continue following up with participants to see whether those infected with the original strain are still reporting symptoms nearly three years later.