Moshe Geva Rosso, 62 years old, receives a fourth dose of the coronavirus disease (COVID-19) vaccine after Israel’s Health Ministry approved a second booster for the immunocompromised, at Sheba Medical Center in Ramat Gan, Israel, December 31, 2021. REUTERS/Nir Elias

Israel on Monday started to jab people above 60 years old and medical personnel with a fourth dose of the COVID-19 vaccine, as the country expects new daily cases of Omicron variant infections to quadruple by the end of the week.

“Israel will once again be pioneering the global vaccination effort. Omicron is not Delta — it’s a different ballgame altogether,” Prime Minister Naftali Bennett said. “We must keep our eye on the ball, act swiftly and decisively if we want to continue engaging and working with an open country as much as possible throughout this pandemic.”

Bennett said Sunday that Israel was facing more than 5,000 verified Omicron variant infections cases a day.

“By the weekend I estimate that we will have crossed the line of 20,000 verified cases and for the peak of the wave, it could be that we will pass 50,000 verified cases. These are very high numbers,” he warned.

Israel’s Heath Ministry Director General Prof. Nachman Ash and Health Minister Nitzan Horowitz on Sunday night gave the go-ahead to administer a fourth dose of the COVID-19 vaccine to all adults over 60, and medical workers, who received the previous dose at least four months ago.

Israel’s Maccabi Health Services said that since the second booster for certain populations was approved, more than 20,000 people had booked a jab. Clalit Health Services, Israel’s largest provider, said several hundreds of people had been vaccinated on Monday and tens of thousands have scheduled to get their fourth shot in coming days.

Although clinical data about the efficacy of a second booster shot remains incomplete, the high infection rate and fast transmissibility of the Omicron variant prompted Israel to be at the forefront of a new vaccination round to protect the most exposed from severe disease. Last week, Israel’s Sheba Medical Center, kicked off the world’s first clinical trial to evaluate a second round of boosters.

“We could reach nearly 10,000 cases by tomorrow. People above 60 years, people with chronic diseases, people who aren’t vaccinated have a higher chance of having severe disease [from] corona and being hospitalized, and the numbers can reach a figure which will be tough for the healthcare system to operate,” Prof. Ronni Gamzu, who served as Israel’s coronavirus czar, told a press briefing Monday.

“The vaccine booster seems less effective against Omicron than it was against Delta, but it protects well against severe cases of COVID-19,” said Gamzu, who is the CEO of Tel Aviv’s Sourasky Medical Center.

Gamzu expects the number of patients needing hospitalization due to the Omicron variant to rise, but estimated that numbers will not be higher than what Israel faced with during the peak of the last wave.

“Almost 1,000 severe cases in hospital, and I believe that it will not go beyond that. This is my speculative forecast,” Gamzu said.

For now, Gamzu said he sees no necessity to extend the fourth COVID-19 vaccine shot to people younger than 60, unless a surge in the rate of hospitalizations is observed among people aged 40-60 who have received the first booster.

“In a way, the Omicron is good news because the high number of people that will be infected by the strain can create the conditions for a natural and gradual herd immunity, with a very low rate of severe disease,” Gamzu remarked. “We will see a higher number of recovered people after Omicron and together with the vaccinated boosted people this may give us a herd immunity.”

“Overall, we are speaking about around 80 percent of people vaccinated and recovered, all together, to reach a rate that the epidemic is not growing but shrinking — although, of course, corona can still have surprises in store for us,” he cautioned.