In the first known research of its kind, medical journal The Lancet published a study on Monday that measured the impact of COVID-19 vaccine mandates in six countries—France, Italy, Israel, Denmark, Germany, and Switzerland—and compared them with 19 countries with no widespread restrictions on unvaccinated people. That latter group includes the U.S., where President Joe Biden’s proposed vaccine mandates have faced fierce opposition in the U.S. Congress.

Judging by most of the countries studied, the vaccine mandates have succeeded in pushing up immunization—in some places, by spectacular rates. The study found that the impact began almost as soon as governments made known their intention to implement restrictions, and before they came into force. “COVID-19 certification led to increased vaccinations 20 days before implementation in anticipation, with a lasting effect up to 40 days after,” wrote the two authors, one a demographer, the other a sociologist, from the University of Oxford’s Pandemic Sciences Center.

The exceptions were Germany and Denmark, which both had an already high vaccination rate, and where mandates had little effect; in Germany, the federal system allowed some states to ignore the country’s vaccine rules, and in Denmark, vaccine doses were in short supply.

But in other countries, the effect was immediate, according to the study.

The Lancet

In France, Israel, Switzerland, and Italy, restricting people’s access to gathering places like movie theaters, bars, restaurants, concert halls, and nightclubs has pushed up vaccination rates among those most impacted by the measures—and in some cases, previously the most indifferent to being immunized. The study found a sharp increase in vaccinations among teenagers and those in their twenties after COVID-19 mandates were introduced.

Most striking of all was the effect of hard-line rules imposed by governments. “Mandatory COVID-19 certification was associated with a sharp increase in vaccination rates before implementation and had a long-lasting effect, with above-average rates after implementation,” the study said.

The prime example, perhaps, is France. Back in July, President Emmanuel Macron became one of the first world leaders to impose vaccine mandates, at a time when the country’s vaccination campaign lagged behind other big economies. Within one month after Macron introduced a nationwide “pass sanitaire,” or health pass, about 3.7 million people raced to be vaccinated; people are required to show their pass, with a QR code, at the door of most restaurants, bars, movie theaters, and concerts, or to undergo frequent COVID-19 tests.

Nearly five months on, about 88% of French over 12 are now fully vaccinated, according to Ministry of Health statistics on Tuesday. That’s one of the highest jab rates in the world, and contrasts with about 60% in the U.S. Macron recently expanded the rules, requiring that all adults get booster shots by mid-January, in order to retain a valid health pass.

In Italy, where the government in September imposed mandatory vaccinations for those working in public settings, vaccination rates shot up 30 days after implementation, “again suggesting a positive relationship between certification and vaccine uptake,” the study says.

Elsewhere, the government’s message was different. After Israel’s COVID-19 infections rose in schools in June, the government there pleaded with parents to have their children vaccinated, and warned that the country’s stock of vaccines were about to expire. The appeal seemed to work: Vaccination rates for those ages 12 to 15 shot up.

Even with strict COVID-19 vaccine rules, however, some people are unlikely to be vaccinated. On Tuesday, France’s Le Monde asked, “With 90% of eligible adults having received one dose, has France reached its vaccine ceiling?” The conclusion: Probably, yes. “The room for maneuver to convince 6 million unvaccinated adults seems limited from here on,” said the newspaper.

The Lancet study agrees, saying imposing COVID-19 rules will not work for all people. “Other measures, such as geographically targeted vaccine drives, or peer-to-peer and community dialogue with low-trust groups to generate understanding might be more effective for certain groups,” it said.