Scientists have recommended daily tests for students who come into contact with Covid cases at secondary schools and colleges after finding that it prevents the spread of infection as much as sending whole bubbles home to isolate.

Researchers at Oxford University compared the two approaches in 201 schools and colleges between April and June this year. Daily testing with lateral flow devices appeared to marginally reduce symptomatic infections in the schools, but had a greater impact on lost education, reducing the number of absences by an estimated 20% to 39%.

The results of the trial, commissioned by the government, suggests that switching to daily lateral flow tests instead of sending contacts of Covid cases home to self-isolate for 10 days may help keep students in school after the summer without exacerbating the spread of the virus.

“In the school setting, it works, it’s safe, and that gives comfort to people who want to work out if there’s an easier way to control the transmission than having “pingdemics” and these rather disruptive waves of controlling the disease,” said Prof Tim Peto, the trial’s principal investigator. The findings have been released in a pre-print.

Dr Bernadette Young, a clinical lecturer in infectious diseases at Oxford, said the trial showed lateral flow tests were “an important part of the toolbox” for schools and colleges.

More than one million children missed school for Covid-related reasons last week, according to figures released by the Department for Education, with secondary schools bearing the brunt of infections and absences. Pupils at secondaries will be expected to take twice-weekly lateral flow tests for at least a month when they return after the summer holidays, and two on-site tests before the start of term.

The Oxford trial randomised schools into two groups. One group continued with standard mass testing and isolation of close contacts of positive cases. The other invited contacts to school for supervised lateral flow tests over the next seven days: those testing negative were able to rejoin their classes.

The researchers drew on gold standard PCR tests to check contacts in both groups for Covid infection. These revealed similar infection rates of 1.6% in the group doing standard testing and isolation and 1.5% in the daily testing group.

Dr David Eyre, an infectious disease clinician at Oxford’s Big Data Institute, said: “It’s important to remember that these tests don’t have to be perfect, they don’t have to pick up every single infection, but if they can pick up infections that are going to spread on to other people, and pick up enough of those, then that is when they can be effective.”

Jonathan Ball, professor of molecular virology at the University of Nottingham, said the study shows how daily testing rather than isolation of contacts is effective in preventing the spread of the virus. “Crucially, it also highlights the unnecessary disruption that isolation rules have had on countless numbers of children.

“Isolation of contacts is an important weapon in infection control, but it is also crude. Rapid testing circumvents needless isolation, and it should be used more widely,” he added.

But Paul Hunter, professor in medicine at the University of East Anglia, said the study could not confirm whether or not either approach actually reduces the risk of transmission. “The conclusions could equally be that both interventions are highly effective or that both interventions have no value whatsoever. It is a shame that the study didn’t have a do nothing control arm, though I suspect they would have struggled to get ethical permission for this, even if they had wanted to,” he said.