JERUSALEM — Israel, which has inoculated a higher proportion of its population against the coronavirus than any other country, is delivering shots so quickly that it is outstripping its supply of vaccine.

Health officials are scrambling to buy more doses and said they may pause giving the first round of shots to younger citizens to deliver the second, final injections to the elderly.

The situation is essentially the opposite of that in many parts of the United States, where vaccine doses are sitting unused as mass inoculation programs struggle to build momentum.

The U.S. vaccination rate is about 1 percent. Israel, with a much smaller population and socialized health care, has reached 12 percent of its residents with the initial dose. Since rolling out the campaign on Dec. 20, Israel has repeatedly surpassed its goal of 150,000 vaccinations a day.

Israel’s head start on the vaccine count does not include almost 5 million Palestinians under its control in the occupied West Bank and the blockaded Gaza Strip, where cases are also surging. Human rights organizations have said Israel is responsible for populations under its control and have called on the country to extend its demonstrated prowess to assist in vaccine programs in the territories.

Israel, which is inoculating residents of Jewish settlements in the West Bank, has rejected claims of human rights groups that it is obliged to provide vaccinations to Palestinians in the territories. Citing the 1990s Oslo peace accords, Israeli officials said the Palestinians bear responsibility for their own health care, although some officials have said they will donate vaccine doses after Israeli citizens have been inoculated.

On New Year’s Day, Prime Minister Benjamin Netanyahu and Health Minister Yuli Edelstein held a news conference celebrating the millionth person to be vaccinated — an inoculation in Umm al-Fahm, an Arab town within Israel’s borders, which, along with other Arab communities, has been among the hardest hit by the virus.

Israeli Prime Minister Minister Benjamin Netanyahu received a covid-19 vaccine on Dec. 19, hours before Israel was set to start mass vaccinations. (Reuters)

“We’re leading in a big way, and we’ll be the first to escape corona!” Netanyahu wrote Saturday in a tweet that included a chart from Our World in Data, a vaccination-tracking website published by Oxford University. It showed that Israel is dramatically outpacing the United States, Canada and several European countries in its national inoculation campaign.

But the success has presented complications — ones other countries might envy — that threaten to slow the government’s drive to vaccinate the majority of the population by March even as the virus threatens to overwhelm hospitals.

Israel, in competition with health ministries around the world, is negotiating to acquire more vaccine or accelerate the delivery of existing orders. At least one shipment of a million doses of the Moderna vaccine will arrive in Israel in early January, rather than in March as was originally planned, according to Israel’s Channel 12 News. But thousands of already-booked vaccination appointments will still have to be postponed, officials said.

Ministry of Health Director General Chezy Levy said over the weekend that while the country remains on track to vaccinate some 2 million people by the end of January, he expects a two-week break in first-dose vaccinations to reserve supplies for the follow-up doses for the elderly and immunocompromised population.

Israel has relied initially on the Pfizer-BioNTech vaccine, manufactured in Belgium and given in two doses spread several weeks apart. Levy said the government is “working intensively” with vaccine firms to deliver more doses.

Vaccine officials are trying to outrace a surging rate of infections. With coronavirus cases topping 6,000 on a recent day and some hospitals close to capacity, the country has just entered a third national lockdown. Experts warn that any slowdown in the vaccination rate could risk additional hospitalizations and deaths.

Health administrators say they are getting mixed messages from the government about how much inventory is on hand and how much can be expected. Some worry that the uncertainty reflects the reluctance of pharmaceutical companies to send more vaccine to Israel as other countries try to jump-start their own programs.

The Ministry of Health warned Sunday that the attention being given to Israel’s initial success is hindering their efforts to buy additional doses, according to media reports.

“I believe that what happened is that companies like Pfizer and Moderna are under pressure from other countries that asked the justified question: Why is Israel able to vaccinate over 11 percent of its population within the first two weeks, while we’re still at something like 0.8 percent?” said Jonathan Halevy, president of Shaare Zedek hospital in Jerusalem, referring to the U.S. vaccination rate.

A Pfizer spokesman said the company may have to shift delivery timelines based on manufacturing capacity and other variables, but not because of outside pressure.

“We have made vaccine doses available as quickly as possible based on the terms of current agreements with individual countries,” Andrew Widger, Pfizer’s Britain-based head of global media relations, said in an email. “These agreements do not impact our commitments to supply other countries where we have agreements.”

Edelstein, the health minister, said all the expected Pfizer vaccine has arrived as planned, although the company was unable to speed up the delivery of the next batch.

“We tried to persuade them to bring the next shipment earlier, but I guess they’re having difficulty with that,” Edelstein said. “My instructions to medical teams are that at any given stage, we will have more vaccine shots in the freezers than what we administrated in the first dose.”

Israel’s vaccine success is made possible by its small size (slighter larger than New Jersey) and the efficiencies of its nationalized health system, in which all 9 million citizens hold identity cards and register their electronic medical files with one of the country’s four national health maintenance organizations (HMOs).

Israel also maintains a national vaccination registry, first designed for childhood vaccinations, that will be used in the coming weeks to monitor immediate and long-term progress of the coronavirus vaccine program.

Those attributes in turn make Israel an attractive pilot case for the pharmaceutical companies. Pfizer, which has a strong presence in the country and an intimate understanding of its universal health-care system, views Israel as a “test case,” said Ran Nir-Paz, an associate professor of infectious diseases at Hadassah Hospital in Jerusalem, “a kind of proof of concept to show that the vaccines work.”

The fast-paced rollout of Israel’s vaccine program has resulted in confusion about who is authorized to receive the shots. People 60 and older are officially eligible, but news outlets and social media posts have reported accounts of younger recipients and VIPs being inoculated.

“Some of the ministers have gotten vaccinated, and we have anecdotal stories of people younger than 60 who got the vaccine, where you ask yourself, how did that happen?” said Ronit Calderon-Margalit, a professor of epidemiology at Hebrew University-Hadassah Braun School of Public Health. “I don’t exactly know how the priorities are being set, so in that sense, there is no transparency.”

The vaccine program, which was launched with Netanyahu getting the first shot on television, has inevitably become enveloped in politics. The program is unfolding as Israel prepares for its fourth general election in two years in March.

Netanyahu is counting on the vaccine program to bolster his popularity, which has plummeted during the pandemic.

In addition to tweeting its progress, the prime minister has repeatedly touted his personal contacts with the heads of Pfizer and Moderna.

But to date, participation in the program has not become polarized by the country’s divisive political schisms. Rather, Nir-Paz said, it has validated the national popularity of Israel’s 70-year-old “extremely socialist” health-care system.

“I think the vaccination campaign has been successful regardless of the politics,” he said. “We’re lucky, with 1 million vaccinated, to be on the other side of this.”