British Prime Minister Boris Johnson warned Monday of a “blizzard” of new coronavirus infections coming into the U.K. from continental Europe, as his government extended the vaccine booster program to younger people in an effort to bolster waning immunity levels during the winter months.

With concerns mounting about a new wave of the pandemic in Europe, the independent body of scientists that makes vaccine recommendations to the British government said people aged 40 to 49 will also be eligible for a vaccine booster shot six months after their initial shot.

Up until now, people aged 50 and over, as well as those working in hospitals and care homes, and younger people deemed to be vulnerable, had been eligible for the Pfizer or Moderna vaccine boosters.

The Joint Committee on Vaccination and Immunization also said that second doses of the Pfizer vaccine have also been approved for 16 and 17-year-olds 12 weeks after their first. There has been no change in the advise for 12-15-year-olds, with the U.K. still only offering a single dose of vaccine.

It said the the broadening of the booster campaign and the offer of a second jab to older teenagers will “help extend our protection into 2022.”

Accepting the recommendations, Johnson urged people to get their booster to get the extra level of protection as pandemic “storm clouds” were gathering over Europe, which has seen fresh lockdowns imposed in Austria and the Netherlands.

“A new wave of COVID has steadily swept through central Europe and is now affecting our nearest neighbours in Western Europe,” he said. “Our friends on the continent have been forced to respond with various degrees of new restrictions, from full lockdowns, to lockdowns for the unvaccinated, to restrictions on business opening hours and restrictions on social gatherings.”

Compared to most other countries in Europe, the U.K. has recorded high, but relatively stable, levels of coronavirus infections in recent months following the lifting of most restrictions in the summer. However, in the past few weeks, a number of European countries have seen sharp infection spikes, prompting renewed concerns about the outlook for the U.K.

“We don’t yet know the extent to which this new wave will wash up on our shores, but history shows we cannot afford to be complacent,” Johnson said.

There have been signs over the past few days of a renewed uptick in cases in the U.K. particularly among students. More than 260,000 confirmed infections were recorded in the past week, up 6% on the previous week.

The government has so far resisted reimposing mandatory laws such as requiring people to wear masks indoors or introducing vaccine passports.

Johnson said there was nothing currently in the data which suggested a need to increase restrictions in England, under its contingency Plan B though he would not rule out more restrictions if the pressure on the National Health Service becomes untenable. Currently, the number of people in hospital with the virus is around 8,500, which though high is far down on the near 40,000 in January. Daily COVID deaths are running at around 150, taking the total to nearly 143,000, Europe’s second highest behind Russia.

A raft of evidence over recent weeks has shown that immunity levels among double-jabbed individuals starts to wane a few months after the second dose of vaccine, though they are still far less likely to suffer severe disease than those who are unvaccinated.

“What’s happening is if you can get your booster then your immunity goes right back up to 95%,” he said. “So far we’ve got 75% of everybody over 70 getting a booster, that’s a huge number of people, but it’s that further 25% that will make all the difference to winter, to Christmas, to our plans going forward, because it’s that extra level of protection that we really need.”

The expansion of the booster program comes as a new study from the U.K. Health Security Agency showed adults over 50 had at least 93% reduced risk of getting a symptomatic case of COVID-19 two weeks after their booster.

The government’s chief medical adviser, Chris Whitty, said more restrictions may be necessary if cases start to rise at the same pace as some countries in Europe.

“They’re not currently going up in the kind of numbers you’re seeing in continental Europe, but obviously if they did that would be a situation where we would have to look again,” he said.

“I think we have got a difficult winter ahead of us,” he added.

(AP)