Experts remain divided over merits of mass Covid tests in schools

By Ian Sample Science editor

The education secretary, Gavin Williamson, has put mass testing for coronavirus at the heart of his strategy to reopen schools after the lockdown. It is a controversial strategy that has divided scientists. Some believe mass testing can help reduce outbreaks at schools, while others argue it could make matters worse by giving teachers and pupils false reassurance.

Mass testing relies on lateral flow tests, or LFTs, which contain antibodies that bind to the virus. When a nasal swab is tested in an LFT, any virus present in the sample sticks to the antibodies and produces a dark band, a bit like a pregnancy test’s indicator. LFTs are not as accurate as the standard NHS lab-based PCR tests, but they are cheap and produce results fast – within 30 minutes.

The downside of LFTs is their performance. In a pilot trial in Liverpool, mass testing failed to spot more than half the people who were infected but had no symptoms. The tests missed nearly a third of asymptomatic people who had high viral loads and were at highest risk of spreading the disease.

Another issue with LFTs is that their accuracy falls in the hands of amateurs. Given that teachers and parents will be administering the tests, this could reduce their value further. In an interim evaluation of the kits, researchers at the University of Oxford and Public Health England’s Porton Down lab found the tests picked up 79% of cases when used by skilled lab scientists, but only 58% when used by self-trained members of the public.

Jon Deeks, a professor of biostatistics at the University of Birmingham, argues that LFTs are not fit for many of the purposes the UK government has in mind, mass testing in schools included. Because the tests miss so many infections, a negative test would not mean a teacher or pupil is virus-free. The danger is that teachers and pupils are falsely reassured and, thinking they are safe, put others at risk. The problem is compounded by letters to parents and guidance for teachers that claim the tests are “very accurate”, he adds. It is not the only concern. Deeks believes that repeated, ineffective testing is a harmful diversion of resources, and risks traumatising children, particularly those with learning difficulties and mental health problems.

Not all scientists are opposed to the testing, however. The Independent Sage committee – not to be confused with the government’s Scientific Advisory Group for Emergencies – concedes that mass testing is not a panacea and will not, on its own, make schools safe. But they back mass testing as a means to find cases of coronavirus, rather than deciding whether or not people are infected. “A negative test should not be taken as an indication that someone is not infected or to relax other mitigations at either an individual or collective level,” the group said in its “safe schools policy” report.

Adam Finn, a professor of paediatrics at the University of Bristol, has made a similar point, saying LFTs are “red light tests” not “green light tests”, meaning that testing negative does not mean a person can behave as if they are virus-free.