The risk for long COVID decreased in patients infected with the Omicron variant of SARS-CoV-2 (B.1.1529) compared with the Delta variant, according to findings published in the Lancet.
Researchers conducted a case-control observational study using self-reported data from the COVID Symptom Study app in the United Kingdom to calculate the relative odds of contracting long COVID during the Omicron period between December 20, 2021 and February 10, 2022 compared with the Delta period between June 1, 2021 and November 27, 2021. The researchers defined long COVID as symptoms that last at least 4 weeks following a COVID-19 infection.
The researchers also analyzed the impact of vaccination timing and age on long COVID. They separated all patients into 3 vaccination groups — those vaccinated within the past 3 months, those vaccinated between 3 and 6 months, and those vaccinated more than 6 months. Additionally, they divided patients by age — those between 18 and 59 years and those 60 years and older.
During the Omicron period, 56,003 adults tested positive for COVID-19, while 41,361 adults tested positive for COVID-19 during the Delta period. Participation in women was higher than in men during both periods (55% for Omicron and 59% Delta cases). A total of 2501 (4.5%) of the 56,003 patients infected with the Omicron variant reported long COVID symptoms, whereas 4469 (10.8%) of the 41,361 patients infected with the Delta variant experienced long COVID.
Regardless of vaccination timing and age, patients infected with Omicron demonstrated decreased risk for long COVID compared with those infected with the Delta variant with an odds ratio ranging from 0.24 (0.20-0.50) to 0.50 (0.43-0.59).
“Omicron appears to cause less severe acute illness than previous variants, at least in vaccinated populations,” the researchers stated. “We believe this is the first peer-reviewed study to report on long COVID risk associated with infection by the omicron variant, highlighting that health surveillance using smartphone apps can produce rapid insights, which we have consistently shown are accurate and subsequently replicated.”
No direct testing of infectious variants occurred since this information was self-reported through a smartphone app database. Assumption of variant depended on time of infection. Additionally, the researchers did not objectively assess duration of long COVID symptoms.
Other study limitations included lack of full generalizability since those with lower socioeconomic status may not have access to smartphone apps, insufficient data on long COVID in unvaccinated individuals, and a shorter period of assessment for the Omicron variant compared with the Delta variant.
Antonelli M, Pujol JC, Spector TD, Ourselin S, Steves CJ. Risk of long COVID associated with delta versus omicron variants of SARS-CoV-2. Lancet. Published online June 18, 2022. doi:10.1016/S0140-6736(22)00941-2