Schools should be allowed to remain closed for the first two weeks of next term, the UK’s biggest teaching union has said, as a leading scientist warned of early signs that a new Covid strain may infect children “slightly more effectively” than previous variants. The National Education Union (NEU) called for online lessons to replace in-person teaching for all but vulnerable pupils and the children of key workers in England’s schools, so that children can be tested. Prof Neil Ferguson, a member of the government’s New and Emerging Respiratory Virus Threats Advisory Group (Nervtag), said preliminary data hinted that the variant could more effectively infect children, though causality had not been established. Speaking to BBC Radio 4’s Today programme, Ferguson, whose modelling led to the first UK lockdown, said: “I think what we’ll see in the next two weeks, while schools are still closed, is probably all the variants of the virus in circulation declining, but we’ll be tracking very carefully whether we can see differences in that rate of decline.” Prof Wendy Barclay, another Nervtag member, explained how the mutations on the variant’s spike protein – the part of the virus that allows it to infiltrate cells in the lungs, throat and nasal cavity by interacting with a receptor called ACE-2 – could explain the potential link in children. “The previous virus had a harder time finding ACE-2 and getting into cells, and therefore adults who have abundant ACE-2 in their nose and throat were easy targets and children were difficult to infect,” she said. “The newer virus has an easier time doing all of that and therefore children are equally susceptible, perhaps, to this virus as adults … It’s not because the virus is specifically targeting them, but it’s just that it’s now less inhibited.” Many secondary pupils in England face a staggered return to class from 4 January to accommodate mass testing in an effort to address the high number of cases among children. The latest data from the Office of National Statistics showed that the Covid positivity rate in England was highest among school-aged children. Data on the new variant’s spread across all age groups suggests it has a growth rate of up to 71% higher than other strains. Based on modelling that incorporated genomic data and results of positive tests, scientists on Monday said they had “high confidence” that the variant appeared to be more transmissible, though causation is unclear. There is no evidence the variant makes Covid more severe or undermines the effectiveness of vaccines, though monitoring is ongoing. Scientists interviewed by the Guardian suggested it was too early to reach conclusions on the variant’s transmissibility in children, particularly given factors such as underlying community infection rates partly due to laxer attitudes to social distancing. “We’ve got to be really careful not to speculate because there’s already a lot of speculation about this particular variant – there’s circumstantial evidence that it’s more infectious but there’s still a lot of work to be done,” said Prof Deenan Pillay, a professor of virology at University College London. Dr Muge Cevik, a member of Nervtag, said: “I think it’s not unsurprising that … if the variant is more transmissible, you would expect more transmission across all age groups … We need to have much more contact-tracing data to understand the relative effects of transmission among the children, so I think the data to analyse this is limited.” Cevik added that it was easier to detect infections in schools because there was more of an appetite for testing compared with sectors where there were economic consequences if workplaces closed down. Closing schools should be the last measure taken, if at all, the scientists argued. “It’s easy to start to think of this variant as a different virus, but no, it’s the same virus. And it’s transmitted in the same way,” said Pillay, suggesting that the focus should be on supporting schools to operate safely. In an open letter to Boris Johnson and Gavin Williamson, the education secretary, the NEU said a two-week delay to in-person teaching should be used to begin vaccinating staff as well as NHS and care workers. Mary Bousted and Kevin Courtney, joint general secretaries of the NEU, said local directors of public health should spearhead mass testing. “We believe that the government could support them via a national advertising campaign to find the staff and volunteers needed, as you did in finding the volunteers to help the NHS at an earlier stage,” they said. “We would hope that such a system could then test all children, at their school site, prior to a return to in-person teaching from 18 January.”