Omicron Less Likely to Cause Long COVID, Data Suggest

The SARS-CoV-2 Omicron variant may pose less risk for long COVID than the Delta variant, U.K. researchers reported.

About 4.5% of people who became infected with SARS-CoV-2 when Omicron was the dominant strain experienced long COVID symptoms, compared with 10.8% who became infected during the Delta period, reported Claire Steves, PhD, of King’s College London in England, and co-authors.

Overall odds of long COVID were about 20% to 50% less during the Omicron era — defined as December 2021 to February 2022 in this study — depending on age and time since vaccination, the researchers wrote in a letter to The Lancet.

“While the risk of long COVID with Omicron breakthrough infection is lower than Delta, given the large number of people infected with Omicron, there will be a significant increase in the number of long haulers as a result of Omicron,” noted Akiko Iwasaki, PhD, of Yale University in New Haven, Connecticut, who wasn’t involved with the study.

“We need to keep our guards up to prevent infection, even if we are vaccinated,” Iwasaki told MedPage Today. “We need to keep our masks on to prevent infection.”

“Ultimately, we need a vaccine that can prevent infection or at least reduce the amount of replicating virus upon infection to prevent long COVID,” she added. “This would require mucosal immunity induced by nasal vaccines.”

The findings were based on self-reported data from the U.K. ZOE Health Study COVID symptom app. The study included people who had a positive real-time PCR or lateral flow antigen test for SARS-CoV-2 after vaccination and no previous SARS-CoV-2 infections before vaccination.

Long COVID was defined by National Institute for Health and Care Excellence (NICE) guidelines as having new or ongoing symptoms 4 weeks or more after the start of acute COVID-19. Participants reported a wide range of symptoms prospectively.

Steves and co-authors identified 56,003 adults who first tested positive between Dec. 20, 2021, and March 9, 2022. These people were referred to as Omicron cases, as more than 70% of cases in the U.K. were attributed to the Omicron at that time. They also found 41,361 adults first testing positive between June 1 and Nov. 27, 2021, referred to as Delta cases.

The researchers included both symptomatic and asymptomatic infections. For the Omicron period, they included only participants who tested positive before Feb. 10, 2022.

Both periods had more women than men (55% for Omicron and 59% for Delta). In both groups, the average age was 53 and the prevalence of comorbidities was 19%.

Among Omicron cases, 2,501 people experienced long COVID. Among Delta cases, that number was 4,469.

For all vaccine timings, Omicron cases were less likely to experience long COVID, with ORs ranging from 0.24 (95% CI 0.20-0.32) to 0.50 (95% CI 0.43-0.59). Results stratified by age were similar.

Even at 4.5%, the potential burden of long COVID is high, Steves noted in a statement.

“The Omicron variant appears substantially less likely to cause long COVID than previous variants but still, one in 23 people who catch COVID-19 go on to have symptoms for more than 4 weeks,” she said.

Limitations of the study include its reliance on self-reported data. There was no direct testing of infectious variants and no objective measures of illness duration, Steves and colleagues acknowledged. The study population may not be fully generalizable to the U.K. population, they added.