Children may need to be vaccinated to ensure their education can continue without disruption, the chief medical officer has suggested.
Asked whether Covid jabs would be rolled out to children, Prof Chris Whitty said the "wider question" was about whether this would help limit the disruption the virus was causing to their schooling.
His remarks come as the head of Britain's biggest teaching union said children should be fully vaccinated before returning to school in September.
If the Government decides to vaccinate schoolchildren, this should happen "as quickly as possible", said Kevin Courtney, the joint general secretary of the National Education Union.
Watch: Government working out a potential plan for children and vaccines, says Matt Hancock
Ministers are awaiting advice from the Joint Committee on Vaccination and Immunisation (JCVI) – which insiders expect will recommend the jab for younger teenagers – before they make a final decision.
The Medicines and Healthcare products Regulatory Agency (MHRA), the UK medicines regulator, has already approved the use of the Pfizer Covid vaccine in 12 to 15-year-olds.
Last month, Matt Hancock, the Health Secretary, announced that Britain had bought enough Pfizer vaccines to inoculate all children over the age of 12.
Mr Courntey told The Telegraph: "If JCVI look at the ethical questions and if they think on the ethical balance – and the MHRA say there is a high degree of safety – then in an ideal world we think it would be better if kids were vaccinated and had three weeks immunity before they come back to school in September."
He described the rising number of cases in schools as a "big problem", adding: "That is where our concern is focused. We do think the disruption to education is a significant factor."
Mr Courtney said he recognised that there are "ethical questions" because children "don't by and large get seriously ill", adding: "So if there is a risk from the vaccine, even if it is an incredibly small risk, an ethical question is raised about whether you give them something with a risk."
Speaking at a Downing Street press conference on Monday evening, Prof Whitty said the key consideration when it comes to vaccinating children is safety.
"We know that the risks in terms of physical disease to children – other than some children with significant pre-existing problems or physical health – are much much lower than for adults," he said.
"So you wouldn't want to vaccinate unless the vaccine is very safe, and vaccines are now being licenced in some countries and we are accruing safety data on the safety of these vaccines in children."
Prof Whitty said any decision should be made "with caution" and went on to explain that there are two possible reasons to vaccinate children.
"The first is those groups that are actually at high risk of Covid, and I think JCVI will be bringing forward advice on this, and those children specifically should be vaccinated to reduce the risk of them having severe disease and in a very small number of cases – but it does happen – mortality," he said.
"But the wider question is around the effect on children's education and the multiple disruptions that might happen and are going to have a very negative impact on their life chances, including the effect it will have on long-term risk of physical and mental ill-health."
A Department of Health spokesman said: "No decisions have yet been made on whether people aged 12 to 17 should be routinely offered Covid-19 vaccines. We will be guided by our expert advisers, and the Government has asked the JCVI for its formal recommendation. We will update in due course."
Watch: COVID-19 cases surging among children