An Israeli woman receives the fourth dose of COVID-19 vaccine at Sheba Medical Center in central Israeli city of Ramat Gan on Dec. 28, 2021. Israel began trials of a fourth dose of coronavirus vaccine on Monday. (Gideon Markowicz/JINI via Xinhua)

An Israeli man receives the fourth dose of COVID-19 vaccine at Sheba Medical Center in central Israeli city of Ramat Gan on Dec. 28, 2021. Israel began trials of a fourth dose of coronavirus vaccine on Monday. (Photo by Gil Cohen Magen/Xinhua)

An Israeli woman receives the fourth dose of COVID-19 vaccine at Sheba Medical Center in central Israeli city of Ramat Gan on Dec. 28, 2021. Israel began trials of a fourth dose of coronavirus vaccine on Monday. (Gideon Markowicz/JINI via Xinhua)