Israel said on Sunday it would begin offering a booster shot of Pfizer Inc’s vaccine to adults with weak immune systems but it was still weighing whether a third round of shots should be given to the general public.

The rapid spread of the Delta variant has sent vaccination rates in Israel back up as new infections have risen over the past month from single digits to around 450 a day.

Health minister Nitzan Horowitz said that effective immediately, adults with impaired immune systems who had received two doses of the Pfizer vaccine could get a booster shot, with a decision pending on wider distribution.

Pfizer and partner BioNTech SE, the main suppliers in a swift Israeli vaccination rollout that began in December, said on Thursday they would ask the US and European regulators within weeks to authorise booster shots.

The two companies cited an increased risk of infection after six months in seeking permission for a third shot.

Drawing criticism from some scientists and officials, the companies did not share the data showing that risk, but said it would soon be made public.

“We are examining this issue and we still do not have a final answer,” Horowitz, speaking on Kan public radio, said about a booster for the general population in Israel.

“In any case we are administering a third shot to people suffering from immunodeficiency. These are for instance people who have undergone organ transplants or suffer from a medical condition which causes a drop in immunity.”

About half of the 46 patients currently hospitalised in Israel in severe condition are vaccinated, according to health ministry data. Israel’s coronavirus pandemic response coordinator, Nachman Ash, said on Wednesday the overwhelming majority of them were from risk groups, over the age of 60 and had prior health problems.

Horowitz said the health ministry would plug a Pfizer supply gap for ongoing two-dose inoculations of the general adult population by using Moderna Inc vaccines already in stock. “We have Moderna vaccines and adults who want to vaccinate can do so from this (Sunday) morning, or maybe tomorrow,” he said.