Some cities in Brazil are providing booster shots of the COVID-19 vaccine, even though most people have yet to receive their second jabs, in a sign of the concern in the country over the highly contagious delta variant. Rio de Janeiro, currently Brazil’s epicenter for the variant and home to one of its largest elderly populations, began administering the boosters Wednesday. Northeastern cities Salvador and Sao Luis started on Monday, and the most populous city of Sao Paulo will begin Sept. 6. The rest of the nation will follow the next week. France, Israel, China and Chile are among those countries giving boosters to some of their older citizens, but more people in those countries are fully vaccinated than the 30% who have gotten two shots in Brazil. A U.S. plan to start delivery of booster shots by Sept. 20 for most Americans is facing complications that could delay third doses for those who received the Moderna vaccine, administration officials said Friday.