(CNN)As Covid-19 cases skyrocketed across Britain in late December, Stuart Guest spent his vacation poring over scientific reports about air cleaning and filtration systems.
Guest, a head teacher at an elementary school in Birmingham, England, scoured Amazon for affordable air purifiers in the hopes of stopping the more transmissible Omicron variant from spreading among his 460 students, who are between 3 and 11 years old.
The British government recommends two models made by Dyson and Camfil, but at £424 ($575) and £1,170 ($1,590), respectively, they were too expensive. Guest ultimately bought £200 ($270) portable units for each classroom.
"I got what I think is the best air purifier for the budget I have available. I hope I've got something that's doing the job, but I'm not an expert. And there's been no guidance put out by the Department for Education. I've had to do it all myself, and I shouldn't have to do that when it's a national crisis," Guest said.
Millions of British students have returned to school following the Christmas and New Year holidays, amid a record surge in infections and hospitalizations. For teachers and parents, the situation has brought a grim sense of déjà vu. Unlike last January, when the rampaging Alpha variant plunged the United Kingdom into another lockdown, Prime Minister Boris Johnson has decided to "ride out" the Omicron wave with limited restrictions and to keep schools open, citing the toll remote education has taken on students' mental health and learning.
But leading teachers' unions say the government hasn't done enough to keep classrooms safe, demanding financial support for air-cleaning units, on-site Covid-19 testing and substitute teaching staff in a rare joint letter.
Ahead of the new term, the Department for Education announced twice-weekly testing requirements and temporary masking for students in middle and high schools, but not for elementary school students. The department said it would be providing 7,000 air-cleaning units for teaching spaces where quick fixes, like opening windows, are impossible -- approximately one for every three schools in England. To plug staffing gaps, the UK's education minister has also suggested combining classes, and called on retired teachers to show "Blitz spirit" to return to the classroom.
"It's woefully inadequate," said Guest of the government's measures. "They keep saying education is their number one priority. It's clear it absolutely isn't." Last Wednesday, five of his staff, including three of his 15 classroom teachers, were out sick or isolating -- the most absent from Guest's school since the start of the pandemic -- and he said he feared more would follow.
As Omicron takes its toll around the world, the ramshackle infrastructure that has kept schools running over the past year is in jeopardy. The variant, which has spurred a record rise in pediatric infections in the United Kingdom, parts of Europe and the United States, threatens to upend the shaky balance that allowed schools to mostly stay open last year -- albeit with targeted classroom closures. It's also cast a harsh spotlight on just how little has been done in some places to protect students, with teachers resorting to propping open windows in freezing weather and frequently checking carbon dioxide monitors while delivering their lessons.
In the US, more children are being admitted to hospitals than ever before. The Biden administration has said schools are "more than equipped" to stay open, as Omicron rips across the country. But some elected officials are erring on the side of caution by delaying the new term, while a teachers' union forced public schools in Chicago, Illinois, to shutter for a week amid criticism from members that conditions in classrooms are dangerous.
Though outbreaks in schools can occur, studies in the UK, Australia, US and Italy have shown that spread among children in school settings is typically lower than -- or at least similar to -- levels of community transmission, when mitigation strategies like masks are in place. But experts are waiting to see whether the more contagious Omicron variant may change that calculus, and trigger an explosion in cases in classrooms.
While children have been less likely than adults to develop