Sage expert Professor John Edmunds said there was a “significant risk of a resurgence” of the virus until all Brits have been jabbed, as he called for the vaccine rollout to turn to children.
Clinical trials are underway on giving jabs to children, but the vaccine is currently recommended for adults.
Health Secretary Matt Hancock said early vaccine data shows the jab can reduce transmission of the virus by two thirds, which could be a factor in deciding whether children get vaccinated.
It comes as Boris Johnson is expected to spell out plans for the return to the classroom on Monday when he unveils his roadmap for exiting lockdown.
Ministers are leaning towards reopening primaries and secondaries on March 8 – despite warnings from education unions that bringing all pupils back at once risks further spikes.
Prof Edmunds, an epidemiologist at the London School of Hygiene and Tropical Medicine, said reopening all schools could push infection rates up.
He told the BBC’s Andrew Marr Show that the virus reproduction rate – known as R – rose above one when schools reopened in November.
Taking into account the progress with vaccines, he said: “If we open schools now, I think the reproduction number is likely to go to be something close to one, potentially slightly above, but it could be around one.”
Prof Edmunds said there was a risk of “major disruption” in schools until children have been vaccinated.
He said: “We’re all at risk and we can all spread the virus, and so until we’ve all been vaccinated – I include children here – then there is going to be significant risk of a resurgence.”
Prof Edmunds, who said he is a father of two secondary age children, said he believes “there is an argument for turning to children as fast as we can” in the rollout.
There will continue to be major disruption in schools until we have vaccinated our children.