Billy Quilty from the London School of Hygiene and Tropical Medicine did four lateral flow tests over about 24 hours and showed how two were negative while two were positive
An expert has shown how quickly Covid lateral flow tests can turn from negative to positive, urging people to wait until just before they go out to do them.
His four separate tests show how a result could be negative and then a few hours later it could be positive.
Billy Quilty, an infectious disease epidemiologist at London School of Hygiene and Tropical Medicine, says the at-home lateral flow tests should be taken just before you go out or mix with others and no sooner.
Mr Quilty warned that a test taken even hours before leaving could be too early.
Taking to Twitter, he shared a photo of four lateral flow tests he had done.
Two tests taken in the morning and at lunchtime were negative.
That evening a very faint positive line showed up on the third test. Then the next morning the fourth test showed a clearly positive result.
“A demo of how fast you can turn positive. Do LFTs *just* before meeting up,” Dr Quilty wrote.
The Government has advised anyone who is heading to an event where they could spread Covid to others to take a lateral flow test first.
As Omicron rips through the UK, with 90,418 positive cases in the last 24 hours alone, people are doing lateral flows before seeing family and friends, before heading to the shops and before going to the pub.
New rules state that anyone who lives with someone who has Omicron must do a lateral flow every day for a week.
Demand for lateral flow tests has massively outstripped supply and many people haven’t been able to get hold of them.
Dr Jenny Harries, chief of the UK Health and Security Agency, said there are enough tests but not enough drivers to deliver them.
From Saturday, an agreement with Royal Mail means double the number of tests will be delivered each day, rising to 900,000.
Lateral flow tests aren’t 100 per cent reliable and don’t always pick up a positive Covid case.
Anyone with Covid symptoms should isolate and take a PCR test to see whether they are positive for the virus.
But despite not always being accurate, lateral flows are still useful and can pick up positive cases. For example they very rarely come out positive if someone is actually negative.
Department of Health figures show a further 125 lives have been lost to the virus today as the new variant continues its “tidal wave” across the nation.
A total of 900 people have been admitted to hospital and in the last seven days that figure totals 6,056. In the past week, 787 people have died within 28 days of contracting the virus, with the official Covid death toll now standing at 147,173.
Another 10,059 cases of the Omicron variant have been reported in the UK, taking the total to 24,968.
Official figures now show that 817,625 people have got their Covid booster jab in the last 24 hours. More than 27 million vaccines have now been delivered in total.
It comes as the government is reportedly drawing up possible plans for a two-week ‘circuit-breaker’ lockdown after Christmas.
Indoor mixing with people who you don’t live with may be banned for two weeks in a bid to slow the spread of Omicron.
Sources have told The Times that ministers will be shown these plans “imminently”.
In a Downing Street press conference during the week, Professor Chris Whitty said: “I am afraid we have to be realistic that records will be broken a lot as rates continue to increase in the next few weeks.”
Prof Whitty said that the full impact of Omicron would be apparent in weeks to come, but painted a bleak picture.
“There are lots of things we don’t know, but all the things we do know are bad,” he said.
“There will be substantial numbers (in hospital), that will become apparent after Christmas… that is a reasonably nailed on prospect.”
George Holan is chief editor at Plainsmen Post and has articles published in many notable publications in the last decade.