The University of Edinburgh academic also warned “a lot of people” could still end up in hospital even if the coronavirus mutation proves to provoke milder symptoms than the Delta variant.
Prof Riley told BBC Radio 4’s Today programme: “Omicron is spreading so quickly that, I think, unless you are living the life of a hermit, you are very likely to come across it in the next few weeks.
“I don’t think anyone should be going around thinking they are not going to catch it, I think that situation has changed.”
She added: “There is a huge ‘if’ about this, ‘is it milder?’. I think it is very dangerous to compare data from South Africa, say, to the UK.
“Even if it is milder and, therefore, a smaller proportion of infected people end up in hospital, given that so many people are going to come across this virus, even a small proportion of a lot of people is a lot of people in hospital.”
On Friday Nicola Sturgeon warned that a “Tsunami of infections” was coming as the new variant takes hold in the UK.
The First Minister advised that Christmas parties should be postponed in a bid to reduce the spread, and issued new guidance stating that all home contacts of a positive case should isolate for 10 days, regardless of vaccination status or initial negative PCR result.