The government is “gambling” on risking the spread of Covid in schools by running controversial trials that do not require some pupils to self-isolate, experts have warned.

In an open letter to education secretary Gavin Williamson, a group of academics and scientists have called on the government to suspend the daily contact testing trials taking place in schools.

It also criticises the decision to include cases of the Delta variant of Covid in the trials and raises concern about how widely consent has been sought across the schools involved.

Tests: ‘Strange’ lack of positive results as schools reopen in full

U-turn: PCR tests to stop false positives grounding pupils

Background: Daily contact testing in schools is halted amid Covid concerns

Under the daily contact testing trial taking place, people who are identified as contacts of a confirmed Covid-19 case are allowed to continue attending as long as they take a daily lateral flow test and get negative results.

Currently, around 200 schools and colleges across England are participating in a trial, with one group following the national guidance of quarantining contacts of positive cases, and the other allowing daily testing of contacts for a week instead of isolation.

As part of the trial, rapid lateral flow tests are to be used each day, with participants also offered a PCR test - which involves sending results to a lab - on days two and seven.

The government had planned to use daily lateral flow tests to replace the need to self-isolate among Covid contacts nationally but abandoned this plan at the beginning of the year on the advice of Public Health England.

A group of scientists and academics have now called for the trials to be halted.

They said that using rapid testing in this way may improve attendance but creates serious risks.

Their letter, published in the BMJ, says that lateral flow tests used for daily rapid testing “cannot detect the lower levels of virus among individuals in early infection”.

It says that the trials therefore risk pupils who produce a false negative test remaining in school and spreading the virus further.

It adds: “Data from contacts in the Test and Trace programme have shown that spread can occur from individuals who had low viral loads at the point of testing.

“Thus there is a high chance that infected contacts in a classroom may be infectious before they are detected as positive by an LFD test.

Government accused of ‘gambling’ on Covid risk in schools

“This trial is gambling on the undetected infectious period in infected contacts being short enough for disease spread not to occur, despite the evidence showing little support for this.” 

The letter adds: “We ask the Department of Health and Social Care (DHSC) to suspend these trials immediately, pending adoption of comprehensive mitigations and to allow time to prepare and provide vital clarity to students, families, teachers, the wider public and the scientific community about the scientific justification and ethical considerations for these trials.

“We would be very concerned about results from these trials being used as the basis for any public health policy, given the assessment of risk of increased transmission arising from these trials is inadequate.”

They add: “It is deeply concerning that the daily contact testing trials are being presented as a solution for educational disruption when so little has been done in the way of basic and highly effective mitigations that would help reduce educational disruption, and investment in catch-up learning to address inequities created by this. 

“Keeping potentially infected and infectious children and staff in school may make attendance numbers look better for the short term, but the risks and potential consequences are very serious.”

A government spokesperson said: “A small percentage of secondary schools and colleges are participating in an independently monitored, voluntary trial of daily contact testing as a replacement for self-isolation, which has been given approval by Public Health England’s Research and Ethics Governance Group.

“The trial concludes at the end of June, at which point the findings will be considered to inform any future use of daily contact testing in schools.”

The trial is voluntary, with only staff and students who have given their consent taking part, the government said.

The letter has been backed by several members of the Independent Sage group including Christina Pagel of University College London, Zubaida Haque, Alice Roberts and Stephen Reicher.

It has also been signed by University of Birmingham academic Jon Deeks who has been a prominent critic of the plan to use lateral flow tests as an alternative to self-isolation. 

In addition, it has been backed by the SafeEdforAll parent campaign group.