A fourth shot of Covid vaccine? Israel tests second booster

Many countries have only recently begun rolling out Covid-19 booster shots, but as the Omicron variant sweeps across the globe, could a fourth dose of vaccine soon be needed? This week, Israel began testing the effects of a "second booster" in a trial at the Sheba Medical Centre, with the country's health ministry already recommending a fourth jab be given to the over-60s and medical workers.