Israel is now requiring anyone over the age of three to show proof of vaccination or a negative Covid-19 test before entering many indoor spaces, as it tackles a sharp rise in infections.
Restaurants, cafes, museums, libraries, gyms and pools are among the venues covered by the "Green Pass" system.
However, proof of immunity is not needed to go into shops or malls.
The country's Covid-19 tsar said it was "at war" with the virus despite its world-leading vaccination programme.
"Our morbidity is rising day by day," Salman Zarka told a parliamentary committee on Wednesday, according to the Jerusalem Post.
The next two weeks leading up to the Jewish New Year festival of Rosh Hashanah on 6 September would be "critical", he warned.
If things did not improve, "we will get to a lockdown like the first and second ones, where we do not go farther than 100 meters from our houses".
Israel has seen a surge of infections driven by the more contagious Delta variant since late June.
The health ministry reported some 7,870 new Covid-19 cases on Tuesday, which was slightly down on Monday's six-month daily record of 8,752.
More than 120 people have died after contracting the virus in the past week - double the monthly total recorded in July - and 600 people are in a serious or critical condition in hospital.
The government has sought to combat the surge by reinstating the restrictions it lifted in mid-June and by bringing back the Green Pass, which shows whether someone has been fully vaccinated, has recently recovered from Covid-19, or tested negative in the previous 24 hours.
Before Wednesday only children aged 12 and over, who have been eligible to get a vaccine since June, and adults were required to present a Green Pass.
It will now also apply to children between the ages of three and 11. Their tests will be funded by the government as they are ineligible for vaccination, unless they are five or older and are considered are at significant risk from Covid-19.
The approximately one million residents - about 11% of the population - who have not been vaccinated despite being eligible must pay for their own tests.
Israel has also begun giving third doses of the Pfizer-BioNTech vaccine to people over 50, medical workers and those with underlying health conditions.
So far, some 1.1 million eligible people have received their booster shots.
Israeli healthcare provider Maccabi, which covers about a quarter of the population, reported on Wednesday that a third Pfizer dose was 86% effective at preventing Covid-19 infection in people over 60.
Mr Zarka also noted that no-one who was currently in a critical condition in hospital had received a booster shot.