JERUSALEM — Israel will begin administering a third dose of the Pfizer-BioNTech coronavirus vaccine those 60 and older, Prime Minister Naftali Bennett announced on Thursday, citing the rising risk of a virus surge fueled by the Delta variant.
The health ministry has instructed the country’s four main health care providers to begin giving on Sunday a booster shot of the Pfizer-BioNTech vaccine to Israelis in that age group who received a second dose more than five months ago. President Isaac Herzog, 60, will be the first to get a booster shot on Friday, Mr. Bennett said.
“The battle against Covid is a global effort,” Mr. Bennett said.
Whether booster shots are needed by older citizens is an issue that is far from settled among scientists. Most studies indicate that immunity resulting from the mRNA vaccines made by Pfizer-BioNTech and Moderna is long-lasting, and researchers are still trying to interpret recent Israeli data suggesting a decline in efficacy of the Pfizer-BioNTech vaccine months after inoculation.
Pfizer on Wednesday offered up its own study showing a marginal decline in efficacy against symptomatic infection with the coronavirus months after immunization, although the vaccine remained powerfully effective against severe disease and death. The company has begun making a case for booster shots in the United States, as well.
The latest government decision in Israel, an early leader in administering vaccines, follows an analysis by the health ministry that estimated that the effectiveness of the Pfizer-BioNTech vaccine in preventing serious illness remained higher than 90 percent — but that its ability to stop infection had fallen over time.
Some experts have pushed back against a rush to approve a booster in Israel. The data are too uncertain, they say, to estimate of how much efficacy has waned. For example, the Delta-driven outbreak hit parts of the country with high vaccination rates first and has been hitting other regions later.
Since June, there has been a steady rise in Israel’s daily rate of new virus cases, and the seven-day average is 1,670 a day. The figure exceeded 2,300 one day this week, a spike that health experts have attributed to the spread of the more contagious Delta variant.
The daily rate is still far lower than at the height of Israel’s third wave of infections in January, when number of new daily cases rose briefly above 11,000. But it is far higher than in mid-June, when the figure fell to single digits and the government eased almost all antivirus restrictions to allow daily life to return to normal.
The number of coronavirus patients in hospitals nevertheless remains relatively low; a total of 159 people were hospitalized on Thursday, much less than the figure of more than 2,000 at the height of the third wave in January.
In the United States, Biden administration health officials increasingly think that vulnerable populations may need additional shots even as research continues into how long the coronavirus vaccines remain effective.
There is growing consensus among scientists, for example, that people with compromised immune systems may need more than the prescribed two doses of the Pfizer-BioNTech and Moderna vaccines. Earlier this month, Israel began administering a third shot of the Pfizer vaccine to people with compromised immune systems. The country has already given 2,000 of those people a third dose with no severe adverse events, Mr. Bennett said Thursday.
Though Israel’s vaccination rate has dwindled in recent months, it was an early leader in the race to vaccinate against the virus, allowing the country to return to ordinary life faster than most other places.
Israeli health care leaders welcomed the decision to administer an extra shot to older citizens, while emphasizing that the original two doses still remained protective against serious illness and death.
Prof. Segal said: “There is no doubt the number of ill is rising. The vaccine’s ability to prevent infection is less, but it is very effective in preventing patients from reaching the point of respiratory failure.”
He added: “I’m under 60, and when I am offered a third dose, I will take it happily.”
Israel has faced scrutiny for its initial reluctance to offer vaccinations to significant numbers of Palestinians living under differing levels of Israeli control in the occupied West Bank and Gaza Strip.
Israel initially said the diplomatic agreements signed in the 1990s with the Palestinian leadership, known as the Oslo Accords, gave the Palestinian health authorities responsibility to procure their own vaccines. Rights campaigners said other clauses of the accords, as well as the Fourth Geneva Convention, gave Israel a legal duty to assist.
But when Israel offered about a million vaccines in June to the Palestinian Authority, which exercises limited autonomy in parts of the West Bank, the authority pulled out of the deal because it said the vaccines would have expired before officials would have had time to administer them. Some of the excess vaccines were later given to South Korea.
Sharon LaFraniere and Carl Zimmer contributed reporting.