One-third of people who are fully vaccinated adults but catch cold-like symptoms may actually be infected with Covid-19, shows a new study.
According to Professor Tim Spector from King's College London, anyone with symptoms, such as a runny nose or a sore throat, must self-isolate and avoid all parties until they receive a negative test result, the Daily Mail reported.
He added that people must "not wait for the loss of smell or taste which may never come, not wait for fever, not wait for that persistent cough".
"At the moment, we're estimating that somewhere between one in three and one in four colds are actually due to Covid," Spector was quoted as saying.
He told Times Radio that the UK must be "much more open-minded about who we are testing" and "get more people to isolate at least for a few days with cold-like symptoms".
"That's quite a high rate of people that are currently not even bothered to get a lateral flow test, or getting a PCR test, going to parties and spreading it around," he said.
"That's quite a high rate of people that are currently not even bothered to get a lateral flow test, or getting a PCR test, going to parties and spreading it around,""So if that transfers to Omicron then we're going to be compounding that problem much faster than we would need to."
Professor Spector said that to curb the spread of Omicron people should stay at home for a few days if they develop any signs of a cold, to be on the safe side.
He added: "That's when you're most contagious, that's when you're most likely to transmit. Whether it's a respiratory virus, you're just giving someone a cold, or you might be giving them Omicron or Delta, then it's those first few days.
"And so we should really be encouraging people not to come into the office, not to go to that Christmas party if they're feeling unwell. Take a test and then, when the symptoms subside, they can come out - it doesn't have to be 10 days but just those first few days are probably the most crucial."
Scientists are hopeful that the Omicron variant will not cause more severe symptoms and that the T-cell immunity provided by vaccines will prevent severe disease, the report said. T-cells are a type of white blood cell that kills Covid.
However, it may take a few weeks time as trials are underway to see how well Omicron evaded immunity from the vaccines.