Moshe Geva Rosso, 62 years old receives a fourth dose of the coronavirus disease (COVID-19) vaccine after Israel’s Health Ministry approved a second booster for the immunocompromised, at Sheba Medical Center in Ramat Gan, Israel December 31, 2021. REUTERS/Nir Elias

Israel is extending its offer of a fourth COVID-19 vaccine dose to elderly people in care facilities, Health Minister Nitzan Horowitz said on Friday, citing their high exposure and vulnerability to infections.

On Thursday, the Health Ministry’s director-general, Nachman Ash, approved fourth doses for people with weakened immune systems and the administering of those shots began on Friday.

An Israeli hospital administered fourth shots to a test group https://reut.rs/3mKSzhq of health workers on Monday, in what it called the first major study into whether a second round of boosters will help contend with the Omicron coronavirus variant.

Results are expected within two weeks. A Health Ministry expert panel last week recommended thatIsrael offer a fourth shot of the vaccine developed by Pfizer and BioNTech to medical workers and those over 60 or with compromised immune systems.

Israel was the fastest country to roll out initial vaccinations a year ago and became one of the first to launch a booster program after observing that immunity waned over time. Its policies on boosters have been closely watched by other nations, including the United States, that are considering when to offer additional doses.