The Prime Minister said there were "storm clouds” gathering over the continent, with some nations imposing new restrictions to try and stem a spike in coronavirus cases.
Speaking at the first UK Government Covid-19 press conference since the conclusion of the COP26 climate summit, Mr Johnson said it was not yet clear the extent to which the “new wave will wash up on our shores”, but stressed “history shows that we cannot afford to be complacent”.
Mr Johnson said there was "nothing in the data" that suggested England was headed for tight restrictions this festive season.
But as Covid cases surge in Europe – in Austria, for example, there are around 1,200 cases per million people based on the seven days to November 14 – he encouraged people to get their booster jab.
"In recent days cases there have been rising here in the UK, so we must remain vigilant, because there is one lesson we can draw from the current situation in Europe,” he explained.
“Those countries with lower vaccination rates have tended to see bigger surges in infection and, in turn, been forced to respond with harsher measures, while those countries with higher vaccination rates have, so far, fared better.
“This shows us once again that if we want to control the epidemic here in the UK, and if we want to avoid new restrictions on our daily lives, we must all get vaccinated as soon as we are eligible.”
He added: “It would be an utter tragedy if, after everything we have been through, people who had done the right thing by getting double vaccinated ended up becoming seriously ill or even losing their lives because they allowed their immunity to wane.”
When pressed over whether the Government could be forced to bring in a Christmas lockdown, Mr Johnson said: “Clearly we cannot rule anything out and the most important thing people can do to prevent further non pharmaceutical interventions from being taken is to get the boosters.”
It has been confirmed all over-40s in the UK will be offered a third dose of a Covid vaccine, after advice from UK Government scientists.
Three doses cuts the risk of infection by more than 93 per cent, according to new data from the UK Health Security Agency.
The Scottish Government has also confirmed people aged between 40 and 49 will be offered Covid booster vaccinations.
Second doses for 16 and 17-year-olds have also been approved after the JCVI said this group should be offered a second jab of the Pfizer/BioNTech jab 12 weeks after they received the first.
The JCVI said the broadening of the booster campaign and the offer of a second jab to 16 and 17-year-olds would "help extend our protection into 2022".
Mr Johnson urged people to get their booster to get the extra level of protection, which will make "all the difference to winter, to Christmas”.
England's deputy chief medical officer Professor Jonathan Van-Tam said everyone had a role to play in helping the UK have "as safe and disruption-free a winter as possible”.
Prof Van-Tam said: "I think for Christmas and the winter period, we can expect respiratory viruses to be around and we are particularly concerned that flu will come back and add to our problems, and it could be quite a bumpy few months ahead.
"But everyone has a key role to play in achieving as safe and disruption-free a winter as possible.
"Wear face coverings in crowded places if it is practical to do so, increase indoor ventilation whenever you can, make sure you are vaccinated and, like any medicine, make sure you finish the course.
"And when you are called for your booster please come forward at pace so that we as a whole UK can get on and finish this job."
He added: "I believe 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 for millions of people."
Prof Van-Tam said experts had seen a "signal" of waning immunity among those aged 40 to 49.
"While the vaccines have fundamentally changed the course of the pandemic in the UK, and the high uptake of the initial programme has saved countless lives and helped restore our freedoms in an unprecedented way, it is also clear that protection will wane over time after the first two doses of a primary course – that is especially so in older adults and those with risk conditions," he said.
"The waning signal, while smaller, is also beginning to show in the 40-49s and without boosting I would not expect it to be static, I would expect it to increase."
Prof Chris Whitty, the chief medical officer for England, told the Downing Street conference the NHS was facing a "difficult winter" as Covid-19 cases continued to rise, with parts of the service were already facing significant pressures.
"I think we have got a difficult winter ahead of us – I think that is a widely accepted situation," he said.
"The NHS is a remarkably resilient organisation. But nevertheless everybody would accept that large parts of it, particularly the ambulance system, but there are others, A&E and others, are under significant pressure, and I'm afraid are likely to remain so over the winter period, which is why all health staff would reiterate the point the PM has made about encouraging people to get vaccinated."