About half of children have already had Covid-19 and the rest are more likely to get it without a vaccine, England’s chief medical officer has suggested.

Professor Chris Whitty warned that “quite a lot of damage” could still occur over the winter months.

He told MPs: “Let’s make an assumption that the great majority of children who’ve not currently had Covid-19 are going to get it at some point over the next period.

“It won’t be necessarily in the next two or three months but they will get it sooner or later.”

But addressing the Commons education committee, Prof Whitty added: “Vaccination will reduce that risk.”

England’s chief medical officer was facing questions from MPs about the inclusion of children in the Government’s Covid-19 vaccination programme.

When asked what proportion of children had already had Covid-19, he replied: “It varies by age and it does also vary by setting, but I think if we go for roughly half I think that is a reasonable stab at this.

“That’s half over the period of the entire epidemic to date, and we’ve got quite a way to run.

“We’re running into winter so there’s still quite a lot of damage that could be done in terms of disruption.”

England’s deputy chief medical officer Professor Jonathan Van-Tam added that because the Delta variant is so infectious “we are not looking at a theoretical risk” of children aged 12 to 17 becoming infected.

He said: “I think it is really quite inevitable that they will be so at some point.”

Prof Van-Tam warned that these pupils could become infected during their GCSEs and A-levels when it is “extremely inconvenient to be laid low” with a cough, fever, and respiratory symptoms.

Addressing MPs, Prof Whitty added: “There is definitely substantial transmission happening in this age group. In fact, the age group we’re talking about is the one in which the highest rate of transmission is currently occurring as far as we can tell.”

Asked about modelling for school days lost due to short-term disruption as a result of the vaccine rollout, Prof Whitty said: “You are not comparing a child being vaccinated against nothing happening.

“You are comparing a child being vaccinated against a near certainty that child will get Covid-19.”

He added: “Our view is firmly that people who have an infection are likely to be off school for longer than people who have a vaccination on average.

“Therefore since virtually any child, unvaccinated, is likely to get an infection at some point between 12 and 15, that is the correct comparison, not against nothing.”

His comments came in the week that the Covid-19 jab is being rolled out to three million eligible youngsters aged between 12 and 15 across the UK.

It is expected to be delivered primarily within schools, and guidance has been issued to headteachers to contact police if they believe protests could be held outside their buildings.

Prof Whitty added that the views of families “should be respected” and children who refuse to get the vaccine should not be stigmatised.

Prof Van-Tam said he had “never once heard” of children being discriminated against because they had chosen not to have an influenza vaccine in school.

He said: “I believe I’m extremely reassured personally by the extreme competence of the system to have avoided that for at least a decade in terms of influenza immunisation.”

Consent letters are being sent out to parents with information on the Covid-19 vaccination.

But parental consent will not be needed if the child is considered competent to make a decision by themselves.

Prof Whitty told MPs: “In general terms, the younger the child the more the absolute assumption would be that if there is a disagreement actually the parents will be the right people to actually turn to for this

“But the two ends of the spectrum in a sense are once you get to 16 there’s a general assumption, and once you get to 18 there’s an absolute assumption, that the person themselves will make a decision.”

He added: “There is a bit of a sliding scale but in practice it’s actually very, very rare that, particularly at the lower age ranges, that this is relevant at all because almost certainly there will be agreement either way and we’re not trying to push this agreement between parents and children.”