Covid lateral flow tests may be less effective at detecting Omicron, US health chiefs have warned.
The Food and Drug Administration (FDA) said new laboratory findings indicated the rapid kits — which give results in as little as 15 minutes — could still spot the highly-infectious variant.
But bosses warned they may have reduced sensitivity, meaning they could wrongly tell more infected people they are free of the virus.
Doubts over the tests come as ministers and health officials in the UK urge people to take a lateral flow test before going out to meet people in an attempt to reduce the chances of people unknowingly passing the virus on to others.
Scores of Britons have complained over the Christmas period that they received a negative lateral flow result only later to test PCR positive.
But the UK Health Security Agency (UKHSA) has insisted that data shows lateral flow tests are just effective at detecting Omicron.
Lateral flow test kits, like the one pictured above are a cornerstone of the Westminster Government’s plans to keep venues like nightclubs and pubs open with ministers urging revelers to take one before heading out to meet others in case they have Covid
The number of lateral flow tests taken in England has risen significantly since the start if December with the 1million mark being breached multiple times as officials urged people to take a test before meeting others
A woman named Angela was one of numerous Britons who have detailed a case where a family member tested negative on a lateral flow test but later positive on a PCR test
Rose Bateman was another, who found herself with a negative result using a latera flow test for Covid but tested positive using a PCR tests later on the same day
Roy from the Hampshire and Surrey Border area claimed to have two family members receive the opposite result of their lateral flow test when later taking a PCR test
The FDA’s statement was based on early data from new laboratory tests involving live samples of the the Omicron virus.
Like the UKHSA, the US agency has been analysing whether lateral flows are just as effective at detecting new Covid variants.
The FDA previously tested the accuracy of the tests using samples of dead Omicron virus, and found they were just as effective.
But now lab tests using live samples of the virus have raised fresh doubts about their accuracy.
‘Early data suggests that antigen tests do detect the Omicron variant but may have reduced sensitivity,’ they said.
However, the FDA is still advising people to use lateral flow tests, saying the findings are still at an early stage.
‘It is important to note that these laboratory data are not a replacement for clinical study evaluations using patient samples with live virus, which are ongoing,’ it said.
‘The FDA continues to authorize the use of these tests as directed in the authorized labeling and individuals should continue to use them in accordance with the instructions included with the tests.’
No data on how less sensitive lateral flow tests may be at detecting Omicron or how many samples of the virus were tested was detailed in the FDA announcement.
Lateral flow tests are a key cornerstone of the UK Government’s plans to keep the hospitality sector open in England over the festive period with officials urging people to take a test before heading out to meet others.
But numerous Britons have cast doubts over if lateral flow tests are accurate enough in recent days following officials advocating for their regular use over the festive period.
One mother described how her son had received five negative lateral flow test but later tested positive on a PCR test.
‘My son has had a positive Covid PCR test, despite five lateral flow tests showing he’s negative. He has all the symptoms of Omicron and feels pretty rough – he’s 25 and super fit,’ she said.
Roy, from Hampshire, also said he had two cases in his family where lateral flow tests had not been accurate.
‘So in the last few days my son had a negative lateral flow test but a positive PCR as he felt a bit chesty. My son-in-law had a positive natural flow test but a negative PCR,’ he said.
UK Health Security Agency (UKHSA) data showed 129,471 people tested positive in England over the last 24 hours, up 43 per cent on last week’s figure of 90,629 — which included case numbers for the other home nations as well
And single mother Rose Bateman also detailed her experience: ‘I tested negative on a lateral flow the morning I took my positive PCR test two hours later, as I had some cold symptoms.’
When contacted by MailOnline about the FDA’s findings, UKHSA referred to data published earlier this month demonstrating that lateral flow tests were just as accurate at detecting Omicron as they were with previous variants.
In its tests the UKHSA used the five lateral flow testing brands dished out by the NHS on samples from patients infected with Omicron.
All of the tests showed a positive result for each patient, even when their sample was diluted, showing the devices have ‘a comparable sensitivity to that observed for previous strains’ of Covid, the UKHSA said.
However, at the time, the UKHSA said it was monitoring how well the tests perform in the real world to ensure their sensitivity is not ‘significantly reduced’ when people swab themselves.
The tests, which can tell if someone is infected in as little as 15 minutes, report positive results by detecting the virus’s nucleocapsid protein.
But this part of Omicron’s cell has four mutations, which has raised concerns that the test could be less effective.
Fears about the accuracy of lateral flow tests and Omicron were first raised by South African experts, where Omicron was first identified.
Dr Angelique Coetzee, chair of the South African Medical Association, told MPs on the Science and Technology Committee: ‘The rapid test still showing false negatives in the early period.
‘We do have patients that waited a week and still have a headache and then they do PCR and it’s positive.’
But despite being urged to take lateral flow tests before meeting up Britons are having increasing trouble securing a supply as the number of kits available dwindles.
Today, pharmacists called for urgent action to improve the supply of lateral flow tests, stating they are being forced to turn people away empty-handed.
The Association of Independent Multiple Pharmacies says people are being turned away every five minutes due to ‘patchy’ supply.
And it said it was frustrating that chemists it represented were having to wait several days for each delivery.
The UK Health Security Agency said it was facing ‘unprecedented demand’ for the tests but insisted it had doubled its capacity since mid December.