IF vaccination is our best route out of the coronavirus pandemic, what can and should we do if uptake is stalling among the young?

In France, a nation known for its vaccine hesitancy, more than 20,000 people a minute - record-breaking numbers - were booking appointments this week within hours of an announcement by President Emmanuel Macron that cafes, restaurants, shopping malls and trains would be out of bounds from August 1 unless customers can present a health pass proving they are either Covid negative or fully vaccinated.

In the United States, everything from free beers and cannabis joints to vaccine lotteries with $1 million prizes have been among the giveaways on offer in a bid to reach maximum immunity.

In Scotland, worries that young people were less likely to act on - or actually receive - appointment letters in the post led to a shift in favour of allowing under-30s to book their own appointments online.

Anyone over 18 yet to receive a first dose has also been urged to visit drop-in clinics, with mobile vaccine units deployed to busy shopping centres in a bid to 'mop up' vaccine stragglers.

READ MORE: Why the Netherlands offers a cautionary tale against the rush to 'freedom'

But in recent days there has been growing evidence that an "uptake ceiling" is being reached.

When Nicola Sturgeon set out Scotland's roadmap to Level Zero and Beyond on June 22, she stated that by July 18 "all adults will have had their first dose".

This was seen as an important milestone to curbing infections as restrictions were eased.

As things stand, however, only 78% of adults aged 18 to 49 have had a first dose and nearly 490,000 remain unvaccinated.

In the 40 to 49 age group uptake has reached 89% and seems to be stagnating there, with just under 1,400 people coming forward since Monday.

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In the 30 to 39 age group uptake of first doses is hovering stubbornly around 80% . There are nearly 142,000 adults in this age band still to be vaccinated, but fewer than 4000 took up the offer of a jag in the past five days.

Among the 18 to 29-year-olds, where uptake is expected to be lowest, larger numbers are still turning out for a first dose - 21,500 since Monday - but that is out of a population of 848,000 of whom 32% still remain completely unvaccinated.

Even among frontline social care workers, more than one in 10 are still unvaccinated - a figure unchanged for weeks.

"You're never going to get 100% uptake, particularly in younger groups," said Professor Linda Bauld, chair of public health at Edinburgh University.

"You see that internationally. There will always be a proportion of people who don't want it and won't get it."

HeraldScotland: Infections, which had been rising most rapidly in young people, are now showing signs of declineInfections, which had been rising most rapidly in young people, are now showing signs of decline

The problem with vaccines is that they have a dual purpose: one is to reduce the vaccinated person's own risk of disease, but the second is to build up population immunity.

The more unvaccinated people there are, the more avenues there are for a virus to continue spreading, mutating, and eventually to infect even fully vaccinated individuals.

READ MORE: Why the Delta variant has left herd immunity through vaccination alone mathematically impossible 

This is particularly likely in people whose immune systems have been weakened, for example by cancer treatment, and who tend to respond less effectively to vaccination.

Given that the Delta variant is roughly twice as transmissible as the original Wuhan strain and more able to cause infections, even in the fully vaccinated, the herd immunity threshold will be harder to reach than ever.

In fact, it may simply be impossible, which is partly why policymakers have switched from talking about elimination to "living with" an endemic virus instead - but even stamping it down to those levels will require an extremely high uptake of around 85% or more of the total population.

HeraldScotland: Paul Offit (inset) believes Covid vaccinations should be made mandatory if uptake falls below the threshold needed to stop the virus spreadingPaul Offit (inset) believes Covid vaccinations should be made mandatory if uptake falls below the threshold needed to stop the virus spreading

For some scientists, vaccination in a pandemic is too serious to be left to personal choice.

"This [Covid] is a contagious disease," said Dr Paul Offit, a professor of vaccinology at the University of Pennsylvania and a member of the US FDA's vaccines committee.

"This is a decision that you're making for everyone with whom you come into contact...if a significant percentage of the population is choosing not to get vaccinated and that allows the virus to continue to spread, then what do you do?

"I think that's when you move to mandates."

Others believe that incentives might hold the key.

Professor Jason Leitch, Scotland's national clinical director, has urged young people keen to travel abroad to consider that, from Monday, holidaymakers returning from amber-list countries can skip quarantine if they are fully vaccinated.

READ MORE: Scotland will move to Level Zero 'with modifications' as outdoor social distancing remains

In England, nightclubs and other crowded venues have been encouraged - but not ordered - by the Government to allow entry only to those with proof of vaccination or a negative test. The industry has so far rejected the plea but, if infections soar, it may be imposed by law instead.

"Having more of these travel freedoms and activities freedoms might incentivise people to take the vaccine," said Dr Antonia Ho, a consultant in infectious diseases and lecturer at Glasgow University.

However, Dr Ho also believes that more could be done to improve the convenience of vaccination for young people.

“Most of the walk-in clinics are 9-5," she said. "You have to make it easy for that age group to get the vaccine. Have evening clinics."

Dr Ho also believes that there is a lingering perception among young people - linked to the AstraZeneca blood clot scare - that getting vaccinated could be more risky than simply catching Covid.

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To dispel this, she said, public messaging should emphasise that not being vaccinated means young people could expose loved ones to the virus.

"I’m seeing young people in their 30s and 40s in hospital, they’re ill enough to be admitted," said Dr Ho.

"A lot of messaging is around personal responsibility, but I think it needs to be more that it’s about protecting others, not just yourself.

"Entire families are getting infected, even people who have one or two doses, and with more indoor mixing I think it's important to communicate that just because your parents are doubly vaccinated doesn’t mean they can’t get it - especially with the Delta variant."

The most recent research from the Office for National Statistics, published on July 2, indicates that only 9% of 18 to 21-year-olds and 10% of 22 to 25-year-olds were actually vaccine "hesitant".

READ MORE: Fear return of schools in August will trigger 'perfect storm' of respiratory viruses

That suggests there are still large numbers who could be "nudged" into vaccination.

But how?

Practical benefits, like plans to exempt fully vaccinated people from self-isolation if they are identified as close contacts, are "definitely a motivator", said Prof Bauld.

HeraldScotland: Professor Linda BauldProfessor Linda Bauld

But could financial rewards also be an option?

“Incentives are a powerful tool for behaviour change," said Prof Bauld, who led the world's largest trial of financial incentives for smoking cessation in pregnancy, which offered women in Greater Glasgow and Clyde up to £400 in shopping vouchers to quit.

It found that cessation rates were significantly higher compared to those receiving only standard treatment of support phonecalls and free nicotine replacement therapy.

"Tayside was the first part of the UK to run an incentive programme for smoking cessation," added Prof Bauld.

"They did it for pregnant women with Asda vouchers, and then they did it for people in the 40% most deprived areas with shopping vouchers.

"Obviously Tayside has been a bit of a hotspot for Covid so I certainly wouldn’t rule that out. You could see a local area deciding that’s what they’re going to do.”

Seeking answers to England's similar vaccination slowdown, Oliver Johnson, a mathematics professor at Bristol University who has won fans for his social media-friendly graphs and statistical analyses of the pandemic, tweeted on Sunday that he would "like to see a weekly lottery with big cash prizes, where everyone who is already double jabbed or has registered two [lateral flow tests] that week can enter".

HeraldScotland: First dose uptake is slowingFirst dose uptake is slowing

The idea is not so absurd: Ohio ran a weekly state lottery from May to June offering university scholarships and $1m jackpots to anyone who had had at least one vaccine dose.

However, an evaluation published on July 2 in the Journal of the American Medical Association (JAMA) found that the Vax-a-Million scheme was not directly associated with an increase in Covid vaccinations and concluded that state-based lotteries generally (there were several copycat initiatives) "are of limited value in increasing vaccine uptake".

Alan J Walkey, a professor of health law and medicine in Boston who led the study, said: "The resources devoted to vaccine lotteries may be more successfully invested in programmes that target underlying reasons for vaccine hesitancy and low vaccine uptake."

There is also evidence, according to the London School of Economics, that offering payments or subsidies for vaccination "might signal risk, and backfire".