A health worker prepares a dose of Pfizer-BioNTech’s coronavirus disease (COVID-19) vaccine as the COVID-19 vaccination campaign continues amid talks of a fourth dose for high-risk groups including those over the age of 60, in Malcha shopping mall, Jerusalem, December 22, 2021. REUTERS/Ammar Awad A major Israeli hospital will begin administering a fourth COVID-19 vaccine shot to 150 staff on Monday in a trial aimed at gauging whether a second booster is necessary nationwide, the facility said on Sunday. Sheba Medical Center near Tel Aviv said its trial would shed light on the efficacy of a fourth dose and help...