Last winter's Omicron variant was less likely to cause lingering symptoms, known as "long Covid", a UK investigation, in The Lancet, suggests.

The King's College London team looked at data from nearly 100,000 people who logged their Covid symptoms on an app.

Just over 4% of those infected during the Omicron wave had logged long Covid symptoms, compared with 10% of those infected in the preceding, Delta, wave.

But as far more were infected during the Omicron wave, the total was higher.

In fact, the much bigger number of new infections during the Omicron wave "entirely trumped" the variant's potential lower risk of long Covid, Kevin McConway, emeritus professor of applied statistics, at The Open University, said.

"Anyway, you don't really have any choice about which virus variant you might be infected with," he said.

"What's more, nothing in these findings tells us what might happen with a different new variant, in terms of long Covid risk."

The researchers tried to take into account other variables, such as how long ago someone had been vaccinated against Covid, but it is impossible to be certain the difference between variants caused the difference in long Covid numbers.

Lead researcher Dr Claire Steves said: "The Omicron variant appears substantially less likely to cause long Covid than previous variants - but still, one out of every 23 people who catches Covid-19 goes 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."

Officials estimate long Covid has affected at least two million people in the UK.

What is long Covid?

While most people who catch Covid don't become severely ill and get better relatively quickly, some have long-term problems after recovering from the original infection - even if they weren't very ill in the first place.

Long Covid isn't fully understood, and there's no internationally-agreed definition - so estimates of how common it is, or what the main symptoms are, vary.

Guidance for health professionals refers to symptoms that continue for more than 12 weeks which cannot be explained by another cause. The Lancet research included symptoms lasting four weeks or more.