Around a third of the U.S. population has been fully vaccinated against COVID-19 after several months of a concerted push to immunize the country.

Vehicles line up in an observation area after receiving a dose of the Pfizer-BioNTech Covid-19 vaccine at a clinic in McClellan, California, U.S., on Thursday, April 1, 2021. Starting April 1, Californians ages 50 and older are eligible to get the Covid-19 vaccine. Photographer: David Paul Morris/Bloomberg via Getty Images