As he urged eligible Britons to take up offers of third jabs "at pace", Professor Van-Tam said the NHS could face a difficult winter as coronavirus remains ‘unpredictable’, despite 12 million booster doses being given.
However, he added that once the country heads out of winter and into spring there would be "calmer waters ahead".
The deputy chief medical adviser said in a press briefing on Monday: “For Christmas and the winter period, we can expect respiratory viruses to be around and we’re particularly concerned that the flu will come back and add to our problems. It could be quite a bumpy few months ahead."
He added: "It's still a time of great delicacy and quite a bit of near-term danger. This virus is unpredictable."
However, Profr Van-Tam said that once the country heads out of winter and into spring there would be "calmer waters ahead".
His words come after the JCVI announced on Monday morning that booster jabs will be rolled out to 40-49 year olds to keep infection levels and hospital admissions down.
The UK has now surpassed 12 million booster doses, and Prof Van-Tam said evidence suggests antibody response and protection pick up occurs "very rapidly" after having the extra jab.
He cited Israel as a promising example of the success of third jabs, with their booster of choice being the mRNA Pfizer jab.
“They’re showing that in people aged over 60 in Israel, after a messenger RNA booster, and compared with simply having received the first two doses of Pfizer – in the case of Israel three to four weeks apart," he said.
"They are observing a tenfold reduction against all COVID infections, an 18.7-fold reduction against hospitalisations, and a 14.7-fold reduction against mortality, and that’s on top of the initial course of Pfizer.
“So I believe therefore that if the booster programme is successful, and with very high uptake, we can massively reduce the worry about hospitalisation and death due to COVID at Christmas, and for the rest of this winter.”
Some 36,517 people tested positive for COVID-19 in the UK on Sunday and there were 63 deaths – with the seven day average at 262,419, up 6%.
Despite Prof Van-Tam's words of caution, this morning Oliver Dowden, co-chair of the Conservative party, told Sky News he was "confident" that Christmas would go ahead as planned.
"I am confident that if we stick the course, people take the boosters when they are asked to do so, that vaccine wall will hold up and we will be able to have a decent Christmas this year," he said.
“There are no plans to stop Christmas happening.
"The huge difference this time is the vaccine.”
Boris Johnson also took an optimistic tone, despite saying earlier this week that there were "storm clouds" over the continent as the virus surges again; Austria have introduced a controversial 10 day lockdown for unvaccinated citizens.
“We don’t see anything in the data at the moment to suggest that we need to go to Plan B, we’re sticking with Plan A," he said.
“But what we certainly have got to recognise is there is a storm of infection out there in parts of Europe, you can see those numbers ticking up very sharply in some of our continental friends.
“And we’ve just got to recognise that there is always a risk that a blizzard could come from the east again, as the months get colder.
“The best protection for our country is for everybody to go forward and get that booster.”
Watch: Jonathan Van-Tam explains where we are in the pandemic 'in football terms'