As Covid-19 infections and deaths in the European Union eclipse those in the U.S., the region is confronting an ugly reality: Defeating the Delta variant is proving harder than a virus-weary continent had hoped.

Fast-rising Covid-19 contagion in parts of Europe, including Germany, is sparking fears of another winter of full hospitals. Countries are rushing to roll out booster shots as evidence accumulates that last summer’s vaccinations are losing some of their efficacy.

Some...

As Covid-19 infections and deaths in the European Union eclipse those in the U.S., the region is confronting an ugly reality: Defeating the Delta variant is proving harder than a virus-weary continent had hoped.

Fast-rising Covid-19 contagion in parts of Europe, including Germany, is sparking fears of another winter of full hospitals. Countries are rushing to roll out booster shots as evidence accumulates that last summer’s vaccinations are losing some of their efficacy.

Some European governments are also raising pressure on unvaccinated people to get shots by tightening the rules for accessing public transportation, shops, restaurants and workplaces. Although the EU has a higher overall vaccination rate than the U.S., vaccine take-up has been uneven across the region.

In some European countries, significant numbers of people remain unvaccinated, including among the older age groups that are most vulnerable. Doctors in Europe say their intensive-care-unit patients are overwhelmingly vaccine holdouts.

The EU has had lower levels of contagion than the U.S. for much of the pandemic, but in the past month, daily confirmed infections have risen fast in the 27-country bloc, to more than 500 per million inhabitants, compared with around 290 in the U.S.

Daily Covid-19 deaths in the EU, at around 3.8 per million inhabitants, have also edged past the U.S. seven-day average level of around 3.4 per million. The EU’s lower ratio of deaths to infections reflects higher vaccination levels, health experts say. Around 67% of the EU’s total population is fully vaccinated, compared with 58% in the U.S.

Protesters from Austria to Italy rallied against new Covid-19 restrictions as police and rioters clashed in the Netherlands. The resurgence of infections is forcing some European countries to reimpose curbs on public life and require vaccinations. Photo: VLN NIEUWS/EPA-EFE/Shutterstock The Wall Street Journal Interactive Edition

“We knew this winter wave was going to come, both because respiratory diseases are worse when it’s cold, and because we saw what happened in Israel this summer when vaccine efficacy dropped off more quickly than expected,” said Carlo La Vecchia, an epidemiologist and professor of medical statistics at the University of Milan. “We can stop this wave of the pandemic by rolling out boosters as quickly as possible, but there are limits to what you can achieve.”

The severity of the rising winter wave varies around Europe. The biggest problems are in a cluster of Central European countries around Austria, Hungary and Slovakia. Vaccine take-up has been particularly low in parts of the continent’s east.

Austria has just begun a three-week lockdown, a throwback to last year that has shaken the confidence of many Europeans who until recently thought they were on a steady road toward normalcy.

In Germany, hitherto not among the worst-hit countries in Europe, politicians and health experts are increasingly debating whether vaccinations should be compulsory for all citizens, challenging the consensus that inoculation has to be voluntary.

German doctors and health experts say the rising number of hospital patients mainly come from the country’s vaccine holdouts—Germany has a relatively high share of older people who haven’t been inoculated, compared with other parts of Western Europe—but also includes some older people vaccinated early this year whose immunity has waned.

Germany’s daily infections and deaths have surpassed those in the U.K., where contagion has remained at a high plateau since the country lifted its pandemic restrictions in July. Some experts say Germany’s relatively low number of total infections since the pandemic began indicates there are still more people susceptible to the virus than in countries that were hit harder.

Workers dismantle a Christmas market booth in the center of Munich, Germany.

Photo: christof stache/Agence France-Presse/Getty Images

Some regions of Germany are tightening the rules for accessing restaurants and other venues, requiring proof of vaccination or recovery from Covid-19, meaning that unvaccinated people can no longer gain entry with a negative test certificate. The policy is aimed at raising the pressure on vaccine holdouts.

In the U.K., government officials and many scientists say mainland Europe is now experiencing the wave the U.K. appears slowly to be emerging from, leading to optimism that Christmas celebrations may be unaffected. The large number of infections in recent months and a program that has delivered boosters to more than 16 million people have given rise to hopes of significant population immunity. Still, cases are running at more than 40,000 a day, and deaths at more than 900 a week.

Government ministers say contingency plans for a reimposition of restrictions are in place if hospitalizations turn sharply upward.

Southern European countries such as Italy and Spain, which suffered some of the world’s highest death tolls when the pandemic began, also have rising case counts, but less dramatically than north of the Alps. Vaccine take-up has been relatively high in Europe’s south, especially among the vulnerable older age groups.

Restrictions are getting tighter again across much of the continent. The Netherlands earlier this month introduced new curbs such as stricter masking requirements, while Belgium is forcing most people to work from home at least four days a week. Both countries faced rioting last week by people protesting the new restrictions.

Even Italy, where some of Europe’s most aggressive rules on vaccinations and mask wearing have slowed the resurgence of infections, Prime Minister Mario Draghi on Wednesday announced stricter measures, including showing a digital Covid-19 certificate—which proves vaccination, recovery or a negative test—for using public transportation.

Earlier this week, 20 small Italian towns in an Alpine province bordering Austria were put under an 8 p.m. to 5 a.m. curfew following a rise in infections in the province, which has one of Italy’s lowest vaccination rates.

Rising health fears and restrictions are slowing Europe’s economic recovery, which was already losing momentum this fall amid the global pressures of supply-chain disruptions and the rising prices of energy and other production inputs.

Europe’s consumer economy is starting to feel the pinch just as the important December holiday season approaches. In some countries, Christmas markets are facing cancellation, while the ski season in the Alps is at risk.

In the affluent city of Munich in Germany’s south, the main Christmas markets, including the so-called Christkindlmarkt on the city’s central square, have been canceled. The markets, famed for their decorated stalls selling mulled wine, roasted chestnuts and gingerbread, were for many people a hoped-for symbol of normalcy.

“Unfortunately, despite the possibility of vaccinations, we are currently far from this normalcy, also because not enough people have been vaccinated,” Dieter Reiter, the city’s mayor, said in a statement last week.

Josef Rohrer, who has run his Alpine-style wooden hut at the Christkindlmarkt for 30 years, said he had already built the structure and hired seasonal workers, spending more than 30,000 euros, equivalent to $33,400, when the closure order came in.

“A second year in a row without a Christmas market is the worst thing that can happen to us,” said Mr. Rohrer. “It’s basically a fatal blow.”

Public-health experts and scientists are pushing governments to speed up the rollout of booster shots, pointing to Israel’s success in taming a surge in infections earlier this year following a booster campaign.

The European Center for Disease Prevention and Control—the bloc’s public-health agency—changed tack this week and advised countries to offer boosters to all adults six months after they were first fully vaccinated. Italy has started injecting booster shots after five months.

In addition, the European Medicines Agency on Thursday said a lower-dose version of the vaccine developed by Pfizer Inc. and BioNTech SE was safe and effective in children age 5 to 11. The recommendation came weeks after the U.S. started vaccinating young children following an endorsement from the Food and Drug Administration.

France has so far resisted the wave of restrictions. In Paris’s Tuileries Garden, next to the Louvre museum, the annual Christmas market opened last week, complete with mulled wine, escargot and a large Ferris wheel. Like Italy, France has since October required proof of vaccination, recovery from Covid-19 or a negative test for many activities, such as dining inside or outside at a restaurant.

French officials said Thursday that they would provide booster shots to all adults and require boosters to keep digital certificates valid longer than seven months after the last dose. Negative tests, an alternative basis for the certificates, will soon have to be less than 24 hours old, rather than 72 hours currently.

French officials also announced a return to mandatory masks in all indoor public spaces, which can be extended locally to crowded outdoor areas such as Christmas markets. Cases are rising, albeit more slowly so far than in Germany. In a sign of the country’s continued struggle to keep a lid on Covid-19, Prime Minister Jean Castex tested positive for the virus this week.

The ski season in the Alps has started with new restrictions. Italy has made proof of vaccination or recovery mandatory for using ski lifts. Until now, a negative test was also accepted. In Austria, despite the lockdown, skiing is permitted, but hotels and restaurants are closed.

In the province of Bolzano in the Italian Alps, the curfew and other measures introduced in 20 towns came after reports of “Covid parties,” where people were deliberately infecting each other to obtain a Covid-19 certificate without having to get vaccinated. Local authorities said they were investigating the reports, including that one party attendee ended up in an intensive-care unit.

“In light of the worrying evolution of the situation, we decided to act in advance to try and avoid worse developments,” said Arno Kompatscher, president of the autonomous Bolzano province.

—Sam Schechner in Paris and Benjamin Katz in London contributed to this article.

Write to Eric Sylvers at eric.sylvers@wsj.com and Georgi Kantchev at georgi.kantchev@wsj.com