JERUSALEM — Israel on Monday began offering anyone over 60 a chance to get a fourth shot of a coronavirus vaccine, greatly expanding a double-booster effort that previously included just older residents with compromised immune systems and some health-care workers.

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       The initiative puts Israel at the forefront of aggressive vaccination strategies as the omicron variant drives up infection rates around the world.

       When officials launched the limited second-booster program last week, they said they were waiting for more data before making it more widely available. But within days, Prime Minister Naftali Bennett said the additional booster shot would be available to anyone 60 or older whose last dose was at least four months ago.

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       “Omicron is not delta,” Bennett said at a late Sunday news conference. “It’s a different ballgame altogether.”

       Booster shots crushed Israel’s delta wave. It’s betting a fourth dose will do the same to omicron.

       Expanding eligibility for the additional dose — the fourth round of shots since vaccinations began a year ago — is meant to protect the most vulnerable from the wave of positive cases that Bennett said could reach 50,000 a day within weeks in the small country.

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       Israel logged more than 6,500 positive cases Monday, the highest daily rate in months, according to Health Ministry figures. More than 100 cities across the country are now operating under their strongest protocols, forcing some students back to remote learning if they have been exposed. Israeli epidemiologists said this week that they expect the omicron variant, which appears to be more infectious but cause less serious illness, to hospitalize about 3 out of every 1,000 infected people.

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       Last week, the government rolled back some of its quarantine requirements for vaccinated people, fearing the rules could affect tens of thousands and lead to a de facto lockdown. Under new regulations, fully vaccinated people can avoid quarantine as soon as they test negative for the virus.

       Israel begins trial of fourth coronavirus vaccine dose ahead of planned national campaign

       Critics have said research is still needed on whether a fourth vaccine dose will be effective. Some have argued that it would be better to focus on reaching the remaining vaccine holdouts. About 6.4 million of Israel’s 9.3 million residents have received their first shot, 5.8 million their second and 4.1 million their third, according to the Health Ministry.