A health expert has explained the best time to do a lateral flow before attending an event or seeing loved ones this Christmas.
Current guidance from the government recommends taking a test "if you will be in a high-risk situation that day".
However, the Manchester Evening News reports that Irene Petersen, a professor of epidemiology at University College London, said official advice should be updated.
READ MORE: Seven Omicron symptoms you should never ignore
Those infected with Omicron, Prof Petersen said, "may switch from being non-infectious to infectious within hours".
She told The Sunday Telegraph: "We’re seeing so many examples now where people have taken a test a day before and then when they take one the day after they are positive.
"Omicron is very, very fast, so the test result expires very quickly. It is hours that we are talking about now."
People are therefore advised to take a lateral flow test as close to the event as possible.
The guidance comes amid reports a circuit-breaker lockdown is being considered from December 27 to combat spiralling case numbers.
The Health Secretary said on Sunday he could make "no guarantees" that more stringent restrictions would not be introduced following "sobering analysis" from scientific advisers warning about the threat from Omicron.
Health Secretary Sajid Javid today told broadcasters: "We keep the data under review at all times.
"It is fast-changing, the situation, there's more data not just here from home but from abroad - we keep an eye on all that data and discuss it with our expert advisers.
"As the Prime Minister has said, whilst there's no need for any further restrictions before Christmas we will certainly keep the situation under review."
On plans for new year, Mr Javid said: "The best advice to everyone is continue to remain cautious and keep looking forward to Christmas."
Asked if Boris Johnson is hiding, Mr Javid replied: "The Prime Minister couldn't be working harder than he is."
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