![A vaccine shot held by a medical professional.](https://www.gpb.org/sites/default/files/styles/flexheight/public/2021-08/covid_vaccine_ap21049403201107.jpg?itok=p1NA56-b)
Caption
A health care worker prepares to administer the Pfizer-BioNTech vaccine, during the start of the COVID-19 vaccination campaign for those in higher risk categories, at a vaccine center in Overijse, Belgium, in February 2021.
Credit: Eric Lalmand, Pool via AP