London Daily

Focus on the big picture.
Wednesday, Oct 08, 2025

When should lateral flow tests be used in England now they must be paid for?

When should lateral flow tests be used in England now they must be paid for?

People may turn to Covid tests less regularly once charges come in from April. When is the optimal time to use one?

For months many of us have used a single red line in a plastic cartridge as a kind of social traffic light – swaying whether go out or stay at home to protect others from Covid. But from 1 April, lateral flow tests (LFTs) for those not showing symptoms will cease to be free of charge in England, and from 18 April in Scotland, meaning people will want to use them as economically as possible (if they bother testing at all). Wales and Northern Ireland are implementing a phased approach to charging for tests.

So, when is the optimal time to test if LFTs are limited and you want the greatest chance of knowing if you’re infected?

Visiting vulnerable friends or relatives


Doing an LFT immediately before visiting a vulnerable person helps to reduce the risk of transmission, but doesn’t entirely negate it. This is because LFTs only produce a second red line (a positive result) above a certain threshold of virus. “You can be infectious without noticing symptoms, or before symptoms develop, and lateral flow tests may miss this,” said Prof Ajit Lalvani, chair of infectious diseases at Imperial College London.

In a recent study published in the BMJ, Lalvani and colleagues found that LFTs would miss 20% of positive cases, when used to screen symptomatic people at an NHS Test and Trace centre, or 29% of cases in city-wide mass testing of asymptomatic people.

Using LFTs as a green light for visiting those at greatest risk of severe Covid could therefore provide false reassurance – although it is better than not testing at all. To further reduce risks, Lalvani advises ensuring that both parties are fully vaccinated; limiting unnecessary social exposure in the five days before the visit; washing hands immediately before the visit; wearing a face mask and maintaining social distancing; and meeting outside or in a well-ventilated room.

You’ve got ambiguous cold-like symptoms but no fever, loss of smell/taste, or cough


According to users of the Zoe Covid app, the most common symptoms associated with the Omicron variant closely match those of common colds or influenza: a runny nose, headaches, fatigue, sneezing and a sore throat.

Although a positive LFT can confirm such symptoms are due to Covid, virus levels may not be high enough during the first few days to give a positive result. This could be a particular issue in people who have been well-vaccinated, because symptoms are often caused by the immune response to the virus, and these responses may kick in faster if you’ve been vaccinated or previously had Covid. This means you may be borderline infectious during the first few days of symptoms – but still testing negative on an LFT.

“The problem is that once the virus starts to replicate it goes really, really fast – so, you may have symptoms in the morning and not be infectious, but by midday you may be infectious,” said Irene Petersen, a professor of epidemiology and health informatics at University College London.

She recommends staying at home if you have any symptoms, and if LFTs are limited, “don’t waste your test at the beginning – keep it until day two or three”.

Staying at home is particularly advisable if you’ve developed symptoms after being in contact with a known Covid case, or local infection numbers are high. If you must leave the house, wear an FFP2 mask, keep your distance from other people, conduct meetings outside where possible, and regularly wash your hands.

You’ve spent time with somebody who definitely has Covid, but you don’t have symptoms


Although there is no longer any legal requirement to self-isolate if you’ve been in close contact with an infected person, the government still advises you to work from home where possible; avoid contact with vulnerable individuals; limit close contact with other people, especially in crowded, enclosed or poorly ventilated spaces; and to wear a mask in these situations.

“After contact with a confirmed Covid case, there is a risk of contracting (and then transmitting) the infection for up to 10 days after the contact,” Lalvani said.

Testing may be advisable in some circumstances, but doing so in the first few days after exposure is likely to be a waste of time (and tests), because it takes time for the virus to produce enough copies of itself to become detectable. According to a recent challenge trial, which involved deliberately infecting 36 young healthy people with the original strain of coronavirus, the average time from first exposure to early symptoms was 42 hours, with virus levels peaking at around five days after exposure, and remaining high for a further four days, on average.

If you never develop symptoms, it’s impossible to know if you’ve escaped infection without testing, so should you use your last remaining LFTs during those five to 10 days after exposure?

“If you do not develop symptoms, then a possible reason for using LFTs after contact would be if you plan to visit a vulnerable person within 10 days of the contact,” said Lalvani. Health or care workers should follow the testing guidelines of their hospital, clinic or care organisation, he added.

You’ve had Covid and are wondering if it is safe to return to work or school


According to current NHS guidance, if you have Covid you should stay at home for up to 10 days from when your symptoms start (day zero), but if you get a negative LFT on days six and seven, and don’t have a fever, you can go back to business as normal. If you have two consecutive negative LFTs, you can be highly confident that you are no longer infectious – so testing at this point is advisable, if you feel well enough to leave the house.

If you continue to test positive after day seven, the picture is less clear. “Often the LFTs continue to test positive even though the person is no longer infectious, but there is no better easily available test to determine the end of infectiousness,” said Lalvani. “Most adults are no longer infectious 10 days after the onset of symptoms, regardless of their LFT results. However, some people, particularly those with health conditions that severely impair their immune systems, may remain infectious for longer.”

Newsletter

Related Articles

0:00
0:00
Close
France: Less Than a Month After His Appointment, the New French Prime Minister Resigns
Hungarian Prime Minister Viktor Orbán stated that Hungary will not adopt the euro because the European Union is falling apart.
Sarah Mullally Becomes First Woman Appointed Archbishop of Canterbury
Mayor in western Germany in intensive care after stabbing
Australian government pays Deloitte nearly half a million dollars for a report built on fabricated quotes, fake citations, and AI-generated nonsense.
US Prosecutors Gained Legal Approval to Hack Telegram Servers
Macron Faces Intensifying Pressure to Resign or Trigger New Elections Amid France’s Political Turmoil
Standard Chartered Names Roberto Hoornweg as Sole Head of Corporate & Investment Banking
UK Asylum Housing Firm Faces Backlash Over £187 Million Profits and Poor Living Conditions
UK Police Crack Major Gang in Smuggling of up to 40,000 Stolen Phones to China
BYD’s UK Sales Soar Nearly Nine-Fold, Making Britain Its Biggest Market Outside China
Trump Proposes Farm Bailout from Tariff Revenues Amid Backlash from Other Industries
FIFA Accuses Malaysia of Forging Citizenship Documents, Suspends Seven Footballers
Latvia to Bar Tourist and Occasional Buses to Russia and Belarus Until 2026
A Dollar Coin Featuring Trump’s Portrait Expected to Be Issued Next Year
Australia Orders X to Block Murder Videos, Citing Online Safety and Public Exposure
Three Scientists Awarded Nobel Prize in Medicine for Discovery of Immune Self-Tolerance Mechanism
OpenAI and AMD Forge Landmark AI-Chip Alliance with Equity Option
Munich Airport Reopens After Second Drone Shutdown
France Names New Government Amid Political Crisis
Trump Stands Firm in Shutdown Showdown and Declares War on Drug Cartels — Turning Crisis into Opportunity
Surge of U.S. Billionaires Transforms London’s Peninsula Apartments into Ultra-Luxury Stronghold
Pro Europe and Anti-War Babiš Poised to Return to Power After Czech Parliamentary Vote
Jeff Bezos Calls AI Surge a ‘Good’ Bubble, Urges Focus on Lasting Innovation
Japan’s Ruling Party Chooses Sanae Takaichi, Clearing Path to First Female Prime Minister
Sean ‘Diddy’ Combs Sentenced to Fifty Months in Prison Following Prostitution Conviction
Taylor Swift’s ‘Showgirl’ Launch Extends Billion-Dollar Empire
Trump Administration Launches “TrumpRx” Plan to Enable Direct Drug Sales at Deep Discounts
Trump Announces Intention to Impose 100 Percent Tariff on Foreign-Made Films
Altman Says GPT-5 Already Outpaces Him, Warns AI Could Automate 40% of Work
Singapore and Hong Kong Vie to Dominate Asia’s Rising Gold Trade
Trump Organization Teams with Saudi Developer on $1 Billion Trump Plaza in Jeddah
Manhattan Sees Surge in Office-to-Housing Conversions, Highest Since 2008
Switzerland and U.S. Issue Joint Assurance Against Currency Manipulation
Electronic Arts to Be Taken Private in Historic $55 Billion Buyout
Thomas Jacob Sanford Named as Suspect in Deadly Michigan Church Shooting and Arson
Russian Research Vessel 'Yantar' Tracked Mapping Europe’s Subsea Cables, Raising Security Alarms
New York Man Arrested After On-Air Confession to 2017 Parents’ Murders
U.S. Defense Chief Orders Sudden Summit of Hundreds of Generals and Admirals
Global Cruise Industry Posts Dramatic Comeback with 34.6 Million Passengers in 2024
Trump Claims FBI Planted 274 Agents at Capitol Riot, Citing Unverified Reports
India: Internet Suspended in Bareilly Amid Communal Clashes Between Muslims and Hindus
Supreme Court Extends Freeze on Nearly $5 Billion in U.S. Foreign Aid at Trump’s Request
Archaeologists Recover Statues and Temples from 2,000-Year-Old Sunken City off Alexandria
China Deploys 2,000 Workers to Spain to Build Major EV Battery Factory, Raising European Dependence
Speed Takes Over: How Drive-Through Coffee Chains Are Rewriting U.S. Coffee Culture
U.S. Demands Brussels Scrutinize Digital Rules to Prevent Bias Against American Tech
Ringo Starr Champions Enduring Beatles Legacy While Debuting Las Vegas Art Show
Private Equity’s Fundraising Surge Triggers Concern of European Market Shake-Out
Colombian President Petro Vows to Mobilize Volunteers for Gaza and Joins List of Fighters
×