London CNN  — 

As the pace of Covid-19 vaccinations in Europe shows signs of a slowdown, leaders are racing to find answers to a key dilemma of the rollout’s next phase: how to convince reluctant citizens to roll up their sleeves.

From cash payments to phone data, free football stadium tours to free grilled meat, officials have offered up a range of carrots to entice people to get shots.

Now, as the Delta variant rips across the continent, threatening to spark another round of lockdowns at the height of summer, some leaders are bringing out the sticks.

In the early hours of Monday, France’s parliament pass a law that requires a “health pass” showing proof of vaccination or a negative PCR test in order to enter restaurants, bars and for travel on long-distance trains and planes, starting in August.

“We will extend the health pass as much as possible to push as many of you as possible to go get vaccinated,” French President Emmanel Macron explained in mid-July, when he announced the legislation. He also said vaccination would be required for health workers from September 15 and hinted at the possibility of making the shot mandatory for everyone if the epidemic worsened.

French President Emmanuel Macron visits a traveling vaccination center in July.

Greece, facing a spike in infections that is threatening the revival of its crucial tourism industry, went a step further than France in mid-July, barring the unvaccinated from indoor restaurants, bars, cafes and movie theaters. It also ordered mandatory shots for healthcare workers.

Italy, which mandated vaccines for health care and pharmacy workers in April, announced Thursday that it too would impose similar restrictions on indoor venues for residents without proof of immunity. “The message that as a government we want to give is, get vaccinated! Get vaccinated! Get vaccinated!” the country’s health minister said.

Barring the unvaccinated from areas of social life is the latest of many restrictions that were once unthinkable in Western democracies but are now becoming commonplace. The moves have sparked protests and renewed the debate about whether getting a shot should be left to individual choice or required by the state for the collective good.

“It’ll be very interesting to see actually how they [Covid-19 certificates] are tolerated because in March 2020, no one thought that you could put a lockdown in Western country and yet that’s exactly what had happened,” Dr. Oliver Watson, a researcher modeling Covid-19 transmission at Imperial College London, told CNN.

It’s also unclear whether coercing people into vaccines will work.

“Previous studies looking at the impact of mandates on vaccine uptake are unlikely to capture the myriad of reasons why vaccine hesitancy related to Covid-19 will be very different to say childhood vaccination mandates for measles,” Watson said.

Will mandates work?

People in Marseille protest on Saturday against vaccine mandates.

Not everyone is behind the patchwork of vaccine requirements. More than 160,000 took part in protests against France’s Covid-19 measures on Saturday, calling for the government to scrap the new rules.

Parisian Axel Miaka Mia was enraged when he heard about the plan. “I am completely against it,” he told CNN on Tuesday. That’s not to say Miaka Mia has taken the pandemic lightly. He has spent the past year worried about the health of his parents and aging family members.

By wielding the stick, the French government will make “many feel like they have to get vaccinated for a somewhat normal life,” he said. But Miaka Mia won’t be getting the shot anytime soon. His workplace does not require him to be vaccinated and he can fit his life around the current rules as it does not apply to small shops.

Experts say it could be difficult to determine the effect that Covid certificates have on vaccine takeup, since such measures are “usually accompanied with more coverage in the media and more discussion surrounding vaccination, which may be as much the cause of changing uptake levels,” Watson noted.

Regardless, Macron’s announcement spurred a rush to get vaccinated, at least in the short term. Doctolib, a French portal to book shots, saw a record-breaking 3.7 million people make appointments in the following week, according to its website.

France’s Minister of State for European Affairs Clement Beaune said the soaring bookings showed “that amongst people that were not vaccinated, a very small minority is anti-vaccination.” It is a statement borne out by recent polling, which shows that the French are warming up to the idea of Covid-19 vaccines after ranking as one of the more skeptical European countries earlier in the pandemic.

The issue of vaccine hesitancy in some European countries goes back years, and “I don’t think the government engagement efforts have dealt with that,” said Dr. Deepti Gurdasani, a public health expert and epidemiologist at Queen Mary University London.

“I think the most successful vaccine programs require an understanding of vaccine hesitancy that’s distinct from anti-vax sentiment,” she told CNN. “Dealing with vaccine hesitancy requires community engagement to actually understand the reasons and address them rather than dismissing people as either ignorant or selfish.”

In Romania, citizens were given traditional grilled minced meat rolls after being vaccinated.

She has strong misgivings about the efficacy of Covid-19 certification schemes when faced with the Delta variant. “With previous variants, we could have achieved herd immunity with high levels of vaccinations but currently we’re dealing with the Delta variant with a reproductive rate (the number of people on average a person with the virus will infect) of six,” she said.

As a result, Gurdasani estimates that 85% of the population will need to be vaccinated for herd immunity to be achieved. “Even with high levels of vaccination, we are not going to stop outbreaks” without other mitigations in place, she said, such as investment in better filtration of indoor environments and a change of culture that prioritizes socializing outdoors instead of indoor environments.

Vaccinating the young

Roughly 55% of all adults in the European Union were fully vaccinated as of Thursday, EU officials announced, meaning the bloc will fall short of its original 70% target by the end of July. Less than half of the population has been fully vaccinated in Germany and France.

In France, people between the ages of 10 and 29 accounted for over half of new cases for the week of July 7. Germany has also seen an uptick in positive cases among younger groups, as well as a lag in vaccination uptake in recent weeks.

Thousands partied in nightclubs across England on July 19 when almost all coronavirus restrictions were scrapped. That same day, UK Prime Minister Boris Johnson announced that vaccine passports would be needed to enter nightclubs by September.

Germany’s politicians have vowed not to impose mask mandates, and it has not rolled out the kind of vaccination incentives pushed out by neighboring countries – although in some German states fully vaccinated people can enter bars or restaurants without a recent negative test, Berit Lange, an epidemiologist at Germany’s Helmholtz Centre for Infection Research, told CNN.

But the country is starting to see an uptick in positive cases among the younger age groups, as well as a lag in vaccination uptake in recent weeks. “Epidemiologists are saying we need vaccinate against this trend otherwise we [could] have a fourth wave similar to what the UK is having,” she said in reference to the skyrocketing cases in the UK, which saw 46,558 test positive for the virus on Tuesday. Germany saw less than 2,000 cases on the same day.

While vaccination rates for younger age groups are lower in general as they only became eligible after older groups, there is growing concern that some young people have become complacent about getting the shot.

In England, home of one of the world’s highest vaccination rates, Prime Minister Boris Johnson loosened nearly all Covid-19 restrictions last Monday, while at the same time announcing that full vaccination would be a condition of entry to nightclubs by the end of September, “when all over 18s will have had the chance to be double jabbed.”

“Though we can see the enthusiasm of millions of young people to get their jabs, we need even more young adults to receive a protection that is of immense benefit to your family and friends – and to yourselves. And so I would remind everybody that some of life’s most important pleasures and opportunities are likely to be increasingly dependent on vaccination,” Johnson warned.

The UK government is now considering making proof of full vaccination against Covid-19 mandatory for all events with more than 20,000 attendees, a government source told CNN on Sunday.

The idea is still in its “early stages” but the English Premier League are expected to be “early adopters” of it if plans are confirmed, the source said.

Experts sensed a note of hypocrisy in leaders targeting younger people with bans on entry to venues like nightclubs. “I think the problem is many of these countries have completely minimized the impacts of Covid-19 on young people,” Gurdasani said. She noted in the UK, three-quarters of all people living with long Covid symptoms were from younger age groups.

In the meantime, the prospect of Miaka Mia getting the jab is close to zero. He instead plans on joining upcoming protests against France’s health measures. “I think that they [the government] really stole our freedom,” he said.

CNN’s Tara John reported and wrote from London. CNN’s Simon Bouvier and Xiaofei Xu reported from Paris. CNN’s Nicola Ruotolo contributed to this report.