Israel will begin offering third doses of the BioNTech/Pfizer Covid-19 vaccine this week to adults with serious pre-existing medical conditions, becoming the first country in the world to officially offer a so-called “booster” of the company’s jab.

The move, confirmed by the health ministry on Monday, comes as US and European health authorities debate the need for booster jabs. Late last month, the UK gave provisional backing for a booster campaign from September. Pfizer last week said it would ask regulators to approve them. Other countries reliant on Chinese vaccines have offered booster jabs.

Israel has been widely hailed for rolling out one of the world’s fastest vaccination drives after it secured regular supplies of the vaccine from Pfizer in return for providing data.

But infection rates are rising sharply in Israel due to the highly transmissible Delta variant. Case numbers have spiked to more than 400 per day, after weeks of single-digit daily infections. However, only 47 out of 4,000 active cases nationally are considered to involve seriously illness, with health experts insisting that the two-dose Pfizer vaccine continues to provide strong protection against hospitalisation and death.

In a statement late last week, Pfizer and BioNTech said that a third dose “has the potential to preserve the highest levels of protective efficacy against all currently known variants including Delta”. The companies were still working on an updated version of their vaccine “that targets the full spike protein of the Delta variant”.

According to Israeli health minister Nitzan Horowitz, a booster would be made available to adults who are suffering from severe immunodeficiency, have undergone a recent organ transplant, or are generally considered at risk.

The health ministry recommends that the third jab should be given between four and eight weeks after the second Pfizer dose, with the approval of a family physician. For some specific at-risk groups, the ministry also recommended that they take an antibody test after both the second and third doses, though it is not a precondition.

“It’s not uncommon in medicine to use drugs ‘off label,’ that is not exactly according to the same protocols as used in clinical studies,” said Dr Eyal Leshem, an infectious disease expert at Sheba Medical Center. “It’s safe, effective and based on clinical judgment.”

Under Israel’s vaccination drive, which began in December, more than 5m of the country’s 9m citizens have been fully inoculated with two doses spread three weeks apart. Health authorities recently launched a push to vaccinate teenagers as well, with about 200,000 over the age of 12 receiving their first jabs over the past two weeks.

After fully reopening its economy in the spring and jettisoning all Covid restrictions last month, Israel recently began reinstating new limitations, including mandating masks for indoor gatherings and public transport. Additional steps, such as stricter quarantine for travellers and greater testing of children, are expected to be introduced. Israel may even bring back the “green pass”, which allowed greater freedom for vaccinated people.

“[Booster shots for at-risk populations are] likely more important than just vaccinating a few 20 year olds,” Leshem added. “It’s plausible you can save more lives with this step.”

This story has been amended to make clear that some countries are offering booster jabs of Chinese vaccines.