Encouraging twice-weekly home testing for Covid-19 for all adults in England and Scotland is a misguided policy that is unlikely to reduce transmission, public health experts have warned in the BMJ.

Public health consultants Angela Raffle and Mike Gill wrote that, without training and proficiency testing for those taking and reading samples alongside a robust process ensuring appropriate actions follow a test result, “SARS-CoV-2 self-testing by asymptomatic members of the public is unlikely to reduce transmission.”

Raffle told Medical Device Network: “Some testing in asymptomatic people is of course essential, for example in an outbreak, for close contacts, in certain workplaces etc. It is the use of testing for millions of low risk people that we are questioning in our editorial. So the cornerstone of testing needs to be for suspected cases, their contacts, and where there is high risk, and all delivered to high quality with support for people who need to isolate.”

The academics said the cost-benefits for testing the nation twice a week are “not known” and “no plans are in place to measure them”, adding that there is no empirical data to support mass screening.

They added that the UK is a global outlier in placing such strong emphasis on asymptomatic testing. The World Health Organization has never advised testing low-risk people, and both the EU and the US Centers for Disease Control and Prevention (CDC) recommend screening tests only for those where risk is highest.

Since 9 April, everyone in England has been eligible for free rapid Covid-19 tests twice a week, while the same policy began in Scotland on 26 April.

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But clinicians remain divided over the efficacy of lateral flow tests (LFTs). While they can give an on-the-spot result within 30 minutes, unlike polymerase chain reaction (PCR) tests which have to be analysed in a lab, they are far less accurate.

The Innova LFT being used in the UK has shown a sensitivity of 58% in people with symptomatic Covid-19. The performance of the device in asymptomatic people is unclear as robust studies on this have yet to be published, but limited pilot data suggests an asymptomatic sensitivity of around 40%.

While a key justification cited by the UK government regarding the mass testing programme is that “up to one third” of Covid-19 cases are symptomless, the tests being used have yet to demonstrate proficiency in detecting asymptomatic cases.

A mounting body of evidence also indicates that transmission arises overwhelmingly from people with symptomatic infections, meaning resources dedicated to rooting out these less common and potentially less infectious cases may be misguided.

While people who have Covid-19 are known to be infectious in the pre-symptomatic stage of the disease, Raffle explains that: “The presymptomatic phase when people are infectious is very hard to find with screening because it is short – which is why focusing on contacts of known cases is more likely to be beneficial.”

Raffle and Gill have also noted that the Covid-19 mass testing scheme could also inadvertently increase the spread of the disease, should a symptomatic person receive a false negative.

While people with Covid-19 symptoms are still required to take a PCR test in the UK, Raffle and Gill wrote: “The temptation for people with symptoms to opt for unsupervised, rapid, and lower sensitivity self-testing may lead to false reassurance, as happens with other screening, leading to potential increases in transmission.”