In the midst of a spike in COVID-19 cases driven by the Omicron variant, Israel announced a preliminary study of its second booster shot had shown some success.
Prime Minister Naftali Bennett announced Tuesday a preliminary study at the Sheba Medical Center found patients who received a fourth vaccine dose had five times more antibodies in their blood.
So far, the fourth shot has only been distributed to immunocompromised people and to people over the age of 60. Israel is likely the first country in the world to provide some citizens with a second booster.
Nachman Ash, director-general of Israel's Health Ministry, said while the government could make second boosters available to more groups of people, he worries it will not come fast enough, as the Omicron variant has been spreading so quickly.
The country reported there were a record-breaking 11,978 new cases Tuesday. Its previous record of 11,345 was reported in September.
However, government records show more severe cases of the virus have stayed constant – possibly an indicator of the vaccine's effectiveness or Omicron's lesser severity. Deaths have also not gone above two in one day since Dec. 13.
About 63 percent of the population has received at least two vaccine doses, with 46 percent receiving a booster. On Sunday, Ash told Radio 103FM "herd immunity," when enough people have been vaccinated against or have recovered from the virus to curb the spread, also poses its own risks.
"The price of herd immunity is very many infections, and that may end up happening," Ash said. "But we don't want to reach it by means of infections."

Israel recently opened to tourists for the first time in nearly two years. After just a month, it slammed shut. Now the Omicron variant has set a widely-expected record for new infections in the country, which will once again crack open on Sunday — but only to travelers from certain nations.
The back-and-forth has created whiplash for many Israelis. Even in the relatively small, wealthy Mideast nation - an early global leader against the coronavirus pandemic - the Omicron variant is outpacing the government's ability to make and execute clear pandemic public policy. What once was a straightforward regimen of vaccines, testing, contact tracing and distancing for the nation of 9.4 million has splintered into a zigzag of rules that seem to change every few days.
The confusion here, on everything from tourism to testing, quarantines, masks and school policy, offers a glimpse of the pandemic puzzle facing governments worldwide as the omicron variant burns through the population. Someday, the World Health Organization will declare the pandemic over. But in the meantime, leaders are weighing how much illness, isolation and death people are willing to risk.
In Israel as elsewhere, what's clear is that the ultra-contagious omicron variant has pushed the fight against COVID-19 into a messier phase of rules governed by a key assumption: Large portions of the public will contract the Omicron version, which is more contagious but appears to cause less severe illness and death, especially among vaccinated people. But vaccinated people are catching the variant too, driving a surge fed in part by gatherings over the winter holidays.
"There is no control of the Omicron wave," said Sharon Alroy-Preis, the Health Ministry's top public health official on Israel's Channel 13 this week.
"Probably no one is protected from infection," said Jonathan Halevy, president of Shaare Zedek Medical Center in Jerusalem on Tuesday.
The new goal is to protect society's most vulnerable people without another national lockdown — the red line Bennett and the country's 7-month-old government are laboring to avoid.
"It's a different ballgame altogether," Bennett said during a press conference Sunday as he warned that the number of daily infections is expected to soar to new records in the coming weeks.
"We must keep our eye on the ball if we want to continue engaging and working with an open country as much as possible," he added.
In everyday life, that's meant a morass of confusion as Bennett and the coalition government he leads struggle to agree on rules and communicate their decisions to the public.
"Education Ministry Leaves Principals to Contend With COVID-19 Chaos Alone," blared a headline in the Haaretz daily Tuesday. A lack of national guidance, the story said, is forcing some school principals to decide on their own whether to hold classes in person, remotely or some combination.
"Most ministries are working together now better than they were under the old government," led by divisive former Prime Minister Benjamin Netanyahu, said Dr. Nadav Davidovich, who heads Ben-Gurion University's school of public health and sits on the national advisory committee on coronavirus.
So the government's decision, for example, to shutter Israel's borders in late November bought time to raise the country's vaccination rates, which rose toward the middle and end of the month. It also allowed hospitals to prepare for a likely wave of illness.
Our World in Data ranks Israel 17th in the world for vaccination rates, behind other wealthy nations like the United Arab Emirates and the United States — and just ahead of archrival Iran. Back in June, Israel was No. 1 on the list.
On Wednesday in the shadow of the record-setting spike of infections, there was more change. Israel's health minister announced that the demand for testing was slowing the results and recommended more at-home rapid testing to ease the burden.
Quarantines that two weeks ago were required of anyone who might have been exposed to the virus are being scaled back in order to prevent the economy from grinding to a halt.
Contact tracing has become more complicated given the shortage of tests.
Israel's list of countries whose tourists are banned has been scaled back, with the Health Ministry on Monday recommending that Canada, France, South Africa, Hungary, Nigeria, Spain and Portugal be removed.
Travel to and from the United States and the United Kingdom remains forbidden.
The Associated Press contributed to this report.