The first-ever vials of the Pfizer-BioNTech and Oxford-AstraZeneca Covid-19 vaccines on display in London. Aaron Chown-WPA Pool/Getty Images In the international race for Covid-19 vaccinations, the U.K. was first to a key milestone. It was the first country to authorize a fully tested Covid-19 vaccine, the one from the partnership of Pfizer and BioNTech. And the country has also embraced a strategy of spacing out vaccine doses to begin immunizing as many people as quickly as possible. The U.K. has now given 34% of its population at least one dose, and about 2% have been fully vaccinated, according to Bloomberg’s vaccine tracker. The U.S. has given 18% of its population at least one shot, and less than 10% are fully vaccinated.