Omicron less likely than wild-type virus to result in long COVID, study suggests

Tired healthcare worker wearing N95

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Swiss researchers find that the SARS-CoV-2 Omicron variant is much less likely to lead to long COVID than the original, wild-type virus.

The research, to be presented at next month's European Congress of Clinical Microbiology & Infectious Diseases (ECCMID) in Copenhagen, Denmark, and not peer-reviewed, found that healthcare workers (HCWs) first infected with Omicron BA.1 were no more likely to have long COVID than their never-infected peers.

The team evaluated the trajectory of long-COVID symptoms in 1,201 previously infected and uninfected HCWs from nine Swiss healthcare networks in March 2021 (Q1), September 2021 (Q2), and June 2022 (Q3).

Participants were regularly tested for COVID-19 and completed symptom questionnaires; uninfected (control) participants were identified through detection of SARS-CoV-2 antibodies. Median participant age was 43 years, and 81% were women. Median follow-up was 18 months.

67% higher odds of long COVID with wild-type

The 157 HCWs infected with the wild-type virus were 67% more likely than uninfected participants to report persistent symptoms, falling to 37% in Q3. The most common symptoms were loss of smell or taste, tiredness/weakness, burnout/exhaustion, and hair loss

A similar pattern was seen in Fatigue Severity Scale (FSS) scores among wild-type–infected HCWs, with a 45% higher risk of fatigue in Q1, declining to 11% in Q3. After wild-type infection, neither Omicron infection nor vaccination affected the outcomes.

The most common symptoms were loss of smell or taste, tiredness/weakness, burnout/exhaustion, and hair loss.

Rates of long COVID among the 429 HCWs with Omicron infections were the same as those of controls for symptoms and 8% higher for FSS. The reason for the similar rates is unknown, lead author Carol Strahm, MD, of Cantonal Hospital St. Gallen, said in an ECCMID news release.

"It's probably due to a combination of the omicron variant being less likely to cause severe illness than the wild-type virus—we know that long Covid is more common after severe illness—and immunity acquired through previous exposure to the virus through, for example, a sub-clinical infection without seroconversion," he said.

In multivariable analysis, the number of long-COVID symptoms at Q1 (adjusted rate ratio [aRR], 5.59) was most strongly tied to symptom number at Q3, but vaccination (aRR, 0.96 per dose) and reinfection (aRR, 1.19) weren't associated.

"With omicron still dominant globally today, our results should provide reassurance to those who are contracting COVID-19 for the first time, as well as those who have already had the wild-type virus," Strahm said. "It is, however, important to note that the participants in our study were mainly healthy, young, vaccinated women, and the results might be different in a sicker, elderly and/or unvaccinated population."

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