Staff volunteers queue to receive a fourth dose of the Pfizer COVID-19 vaccine at Sheba Medical Center in Israel on Dec. 27, 2021, as the hospital conducted a trial of a fourth jab of the vaccine.
Jack Guez/AFP via Getty Images
This colorized transmission electron micrograph image shows SARS-CoV-2, the coronavirus that causes the disease COVID-19. This specimen was isolated from a patient in the United States. Particles of the virus (yellow) are emerging from the surface of cells cultured in the lab (pink).