An Israeli hospital administered fourth COVID-19 vaccine doses on Monday to a test group, as the country considers approving the measure for vulnerable populations in a bid to outpace a surge in infections fueled by the Omicron variant.

The Sheba Medical Centre study in Ramat Gan outside Tel Aviv "will zero in on efficacy of the vaccine in producing antibodies, and safety, in order to ascertain if a fourth vaccine is needed in general," a spokesman said.