People in Israel must now show proof they have received three COVID-19 vaccinations if they wish to enter restaurants, bars, gyms and other venues, as the nation becomes the first to make booster shots a requirement for its vaccine passport system.

Israel became a global frontrunner in vaccine distribution earlier this year, and the nation has now charged ahead with an expansive booster campaign that has moved beyond at-risk groups to include all those above the age of 12 years old.

The country operates a vaccine certification system called the green pass, in which people must show proof of full vaccination or that they have recently recovered from the virus to gain entry into many venues. Proof of two vaccinations was sufficient until this week, when health authorities installed the more strict classification for full immunity in order to encourage people to get boosters.

Around 70 percent of all current serious COVID-19 cases in Israel are among unvaccinated people, according to the country's Health Ministry.

"We are at a critical stage," Israel Prime Minister Naftali Bennett said in a statement on Saturday. "It is precisely now that we must be strict about the green pass, be careful and not become complacent. The vaccine saves lives, and the extent of the country's vaccination is what allows it to remain open and functioning."

The new requirement means that an estimated 2 million people will now lose their green pass until they receive a third shot, barring them from most social venues as well as many workplaces. Some in Israel have criticized the strict rules, saying that the nation's vaccination program has essentially become mandatory in all but name.

The original green pass system was due to expire on Sunday; however, demand for new passes crashed the government website. The Health Ministry said that existing passes will therefore remain valid over the coming days.

Several nations that are considering their own booster campaigns are closely monitoring data from Israel. Last month, a cohort of Israeli health institutes published a study in the New England Journal of Medicine, which found that people over 60 years old who had received a third shot were 19.5 times less likely to develop severe COVID-19 when compared to people in the same age group who had been double jabbed.

European Union drug regulator the European Medicines Agency is expected to issue a recommendation for or against boosters on Monday.

Some EU nations have already moved ahead independently with boosters, including Italy, France, Germany and Ireland. The United Kingdom has also commenced distribution of third shots among health workers and at risk groups. A number of vaccine equality campaigners and international health bodies have questioned the need for third jabs at this point in the pandemic, when vaccine supply is limited and billions of people are yet to receive a first treatment.

The World Health Organization has repeatedly called on rich nations to suspend the distribution of boosters until vaccination coverage has increased in low-income countries.