Symptoms of COVID-19 in patients infected with the Omicron strain of the virus are "rather different" from those caused by earlier strains and the still-prevalent Delta, a UK advisor on COVID-19 has said.

Speaking on Radio 4's Today Program, Regius Professor of Medicine at the University of Oxford and a UK Government advisor on COVID-19, Sir John Bell, said that data from South Africa, as well as the ZOE COVID-19 symptom study, showed that Omicron appeared to be "behaving significantly differently" in regard to the clinical picture.

The data, which he stresses only shows us the early stages of the disease, due to the small amount of time that has elapsed since Omicron's discovery, appears to suggest there are some new signs to look out for, that were less prevalent in earlier strains, such as Alpha and Delta.

"I think one of the few things we do know is the syndrome is rather different. We do know that it's behaving rather differently. It looks like the symptoms of this are stuffy nose, sore throat," he said on the program on Tuesday, adding "myalgia – which is basically aching muscles – particularly around the back are very characteristic of this, and no-one knows why that is."

"People also have a bit of gut upset. They have a bit of loose stools, those sort of things."

The picture is, of course, still evolving, and the US Centers for Disease Control and Prevention currently writes that the most commonly reported symptoms are "cough, fatigue, and congestion or runny nose", though – like with other variants – this will likely change as more data comes in.

Bell went on to say that we still do not know a lot about Omicron, particularly with regards to later stages of the disease, though we will soon get an insight into this as data comes in from South Africa, where the variant was first identified.

"We know this is a highly, highly infectious variant. Two to three times more infectious than Delta, which was already a pretty infectious variant on its own," he said in the interview. "What we're still waiting for is the data of what is the consequences of that [...] from a clinical perspective."