Israel on Thursday approved a fourth vaccine shot for vulnerable people, becoming one of the first countries to do so, amid a surge in Covid in cases driven by the Omicron variant.
The approval came as another anti-Covid weapon arrived in the country: a first shipment of Pfizer's anti-Covid pills.
"Today I approved giving the fourth vaccine for immunocompromised people," health ministry director-general Nachman Ash told reporters.
"I did this in light of studies that show the benefit of the vaccine, including the fourth vaccine, to this population, and in light of the fear they are more vulnerable in this outbreak of Omicron."
Health authorities reported on Thursday more than 4,000 new cases, a high not seen since September.
Health Minister Nitzan Horowitz said Israel was in "a fifth wave", with most cases probably related to the Omicron variant.
Prime Minister Naftali Bennett said Israel, which was among the first countries in the world to offer a third shot to the general public, would be a trailblazer for the fourth jab.
"Israel will lead the way in administering a fourth vaccine to the Israeli people," he said.
Some 4.2 million people out of a population of 9.4 Israelis have gotten three shots of coronavirus vaccine.
Also on Thursday, an Israeli El Al flight from Belgium landed in Tel Aviv carrying a shipment of Pfizer's anti-Covid pill, Paxlovid.
Bennett hailed this as an "important addition to the arsenal in the war against the pandemic".
"Thanks to our rapid action, the drugs have arrived in Israel quickly and will assist us in getting past the peak of the coming Omicron wave," he said.
Ran Balicer, chairman of Israel's national expert panel on Covid-19, said the Pfizer drugs could "dramatically reduce risk of severe illness, potentially thus also reducing the overall hospital burden".
He said the medications were critical, "in addition to vaccines and masks".
The US Food and Drug Administration last week authorised Pfizer's Paxlovid pill for high-risk people aged 12 and up.
In trials, the treatment has been shown to reduce Covid hospitalisations and deaths by 88 percent among at-risk people.
The oral treatments block the virus' ability to replicate and should withstand variants, experts say.
Until now, the main treatments for Covid have been synthetic antibodies or Gilead's antiviral remdesivir, which are administered by infusion.
The United States has paid $5.3 billion for 10 million courses of Pfizer's new treatment, as well as $2.2 billion for treatment from rival Merck, whose pill appears to be less effective.
The European Union's drug regulator has also allowed member states to use Pfizer's Covid medications ahead of formal approval as an emergency measure.
Ash approved the booster after Israel's Sheba Medical Centre launched a clinical trial Monday, giving 150 staff members a fourth jab to test the benefit of a wider national rollout of additional doses.
He also announced new health regulations, requiring people to wear masks at outdoor gatherings of more than 50 people.
Israeli health authorities have shied away from sweeping social distancing guidelines and lockdowns seen in the earlier days of the pandemic.
The government has also not blocked large gatherings for New Year's Eve.
Horowitz said, however on Thursday, "every person must take personal responsibility."
"We will not station an inspector and we won't send a police officer to every person."
Last week Chile announced it would offer a fourth shot to at-risk people beginning in February. Health authorities in the United Kingdom and Germany have also said they are considering fourth doses.