The Omicron variant of COVID-19 is less likely to cause long COVID risk than the Delta variant, new research in the UK has found.

Analysis by researchers from King's College London of data from the ZOE COVID Symptom study app published on June 16 in a letter to The Lancet journal found the odds of experiencing long COVID were between 20-50 per cent less during the Omicron period versus the Delta period, depending on age and time since vaccination.

Long COVID is defined by the UK's National Institute for Health and Care Excellence (NICE) guidelines as having new or ongoing COVID symptoms four weeks or more after the start of the disease.

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 four weeks, said the lead author of the study, Dr Claire Steves from King's College London.

Given the numbers of people affected it's important that we continue to support them at work, at home and within the NHS [National Health Service], she said. Long COVID symptoms include fatigue, shortness of breath, loss of concentration and joint pain and these are said to adversely affect day-to-day activities, and in some cases can be severely limiting.

Patient surveys suggest a range of other symptoms may also be present, including gut problems, insomnia and vision deterioration. This week's research is based on the first peer-reviewed study to report on long COVID risk and the Omicron variant.

King's College London studied 56,003 British adults infected between December 2021 and March this year, when Omicron was dominant, comparing them with 41,361 cases when Delta was prevalent.

The UK's Office for National Statistics (ONS) has found that five per cent of people reported at least one long COVID symptom 12 to 16 weeks after a coronavirus infection.