Summary: New research indicates that people infected with the Omicron variant of COVID-19 have a 20–50% lower chance of developing long COVID compared with infections that occurred during the Delta wave.
Source: King’s College London
Omicron appears less likely than Delta to lead to long COVID, according to a new peer-reviewed analysis.
Researchers at King’s College London analysed symptom data collected through the ZOE COVID Symptom Study app and published their findings in a letter to The Lancet. This study is the first peer-reviewed assessment reporting the comparative risk of long COVID following infection with the Omicron variant versus the earlier Delta variant.
Long COVID is defined by the UK’s National Institute for Health and Care Excellence (NICE) as new or persisting symptoms that last for four weeks or more after the initial onset of COVID-19. Common symptoms include persistent fatigue, breathlessness, problems with concentration (often described as “brain fog”), and joint or muscle pain. For many people these symptoms interfere with everyday activities, and for some they can be severely disabling.
The King’s College London team evaluated outcomes for two distinct time periods: cases that first tested positive between 20 December 2021 and 9 March 2022, when Omicron was dominant, and cases first testing positive between 1 June 2021 and 27 November 2021, when Delta predominated. The study identified 56,003 adult UK cases in the Omicron period and 41,361 adult UK cases in the Delta period.
Across the cases analysed, 4.4% of infections during the Omicron period were classified as long COVID, compared with 10.8% of infections during the Delta period. Depending on factors such as age group and the time since vaccination, the odds of developing long COVID after an Omicron infection were estimated to be between 20% and 50% lower than after a Delta infection.
Despite the reduced odds on an individual level, the overall number of people living with long COVID rose during the Omicron wave. This apparent contradiction is explained by the much larger number of people infected during the Omicron surge from December 2021 to February 2022. The UK Office for National Statistics estimated that the total number of people experiencing long COVID increased from 1.3 million in January 2022 to around 2 million by 1st May 2022.
Lead author Dr Claire Steves of King’s College London emphasised both the encouraging and the concerning aspects of the findings: “The Omicron variant appears substantially less likely to cause Long-COVID than previous variants but still 1 in 23 people who catch COVID-19 go on to have symptoms for more than four weeks. Given the numbers of people affected it’s important that we continue to support them at work, at home and within the NHS.”
These results add important information for public health planning and for individuals weighing the risks associated with different variants. While reduced individual risk of long COVID with Omicron is reassuring, the scale of infections during a wave strongly influences the total burden of long-term illness on health services and society. Continued monitoring of long COVID outcomes, vaccination effects, and variant-specific risks remains essential for guiding health policy and patient care.
About this Long-COVID research news
Author: Tanya Wood
Source: King’s College London
Contact: Tanya Wood – King’s College London
Image: The image is in the public domain
Original Research: The findings will appear in The Lancet