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, AP reports.

Rio de Janeiro, currently Brazil's epicentre for the variant and home to one of its largest elderly populations, began administering the boosters on Wednesday.

Northeastern cities Salvador and Sao Luis started on Monday, and the most populous city of Sao Paulo will begin from Sept 6. The rest of the nation will follow next week.