Slovakia, the Czech Republic, the Netherlands and Hungary all reported new highs in daily infections as winter grips Europe and people gather indoors in the run-up to Christmas, providing a perfect breeding ground for COVID-19.
The disease has swept the world in the two years since it was first identified in central China, infecting more than 258 million people and killing 5.4 million.
The European Centre for Disease Prevention and Control (ECDC), the EU public health agency, recommended vaccine boosters for all adults, with priority for those over 40, in a major shift from its previous guidance which suggested the extra doses should be considered for older frail people and those with weakened immune systems.
"Available evidence emerging from Israel and the UK shows a significant increase in protection against infection and severe disease following a booster dose in all age groups in the short term," the ECDC said in a report published on Wednesday.
Many EU countries have already begun giving booster doses to their populations but are using different criteria to make priorities and different intervals between the first shots and boosters.
ECDC head Andrea Ammon said boosters would increase protection against infection caused by waning immunity and "could potentially reduce the transmission in the population and prevent additional hospitalisations and deaths".
She advised countries with low levels of vaccination to speed up their rollouts and warned of high risks of a further spike in deaths and hospitalisations in Europe in December and January if the recommended measures are not introduced.
World Health Organization chief Tedros Adhanom Ghebreyesus, acknowledging that Europe was again at the epicentre of the pandemic, warned against a "false sense of security" over the protection offered by vaccines.
"No country is out of the woods," he told reporters, adding that he hoped a consensus can be found at a World Trade Organization ministerial meeting next week for an IP waiver for pandemic vaccines, already supported by more than 100 countries.
Sweden will begin gradually rolling out boosters to all adults, government and health officials said. Booster shots of mRNA vaccine have been offered to people aged 65 or above, with an eye to eventually extending the shots to other groups.
"We are faced with an uncertain winter," Health Minister Lena Hallengren told a news conference. "You can contribute by staying home if you're sick or by getting vaccinated if you haven't already, and taking your booster when you're offered it."
Slovakia reported its highest daily rise in cases on Wednesday when the government approved a two-week lockdown, broadcaster TA3 and other media reported, citing Economy Minister Richard Sulik, to quell the world's fastest surge in infections.
Neighbouring Austria has already locked down its population this week for at least 10 days, becoming the first to reimpose such restrictions. It will also require the whole population to be vaccinated from Feb. 1, infuriating many in a country where scepticism about state mandates affecting individual freedoms runs high.
The Czech Republic reported its highest daily rise in infections, with cases surpassing 25,000 for the first time and putting further strain on hospitals. The government is looking to institute mandatory vaccines for people over 60 and some professions, like healthcare workers.
The Netherlands recorded more than 23,700 coronavirus infections in 24 hours, the highest number since the start of the pandemic, and the government will announce new measures on Friday.
Hungary reported a record 12,637 new daily COVID-19 cases.
Prime Minister Viktor Orban's government, which opposes further lockdowns for fear of stifling the economy, launched a vaccination campaign this week, offering shots without prior registration.
But the idea of mandatory vaccinations has also raised concerns among Hungarians.
Authorities in Russia, where daily coronavirus-related deaths are near record highs, said they were scouring social networks and media websites to find people spreading false claims about the dangers of vaccination, the latest in a series of measures to invigorate sluggish inoculation rates.
France will announce new COVID containment measures on Thursday as the infection rate surges nationwide.
Italy is expected to restrict access to some indoor venues for people who have not been vaccinated.
Poland will have to tighten restrictions if it does not see daily case numbers decreasing in the near future, the health minister said.
Many German regions have already started to impose tighter rules amid the country's worst COVID surge yet as the curtain comes down on the Angela Merkel era, including demanding that vaccinated people show a negative test to attend indoor events.
Outgoing Health Minister Jens Spahn said on Monday that by the end of the winter almost everyone in Germany would be "vaccinated, recovered or dead".