SAO PAULO, Brazil (AP) — 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 epicentre 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 September 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 per cent who have gotten two shots in Brazil. A US plan to start delivery of booster shots by September 20 for most Americans is facing complications that could delay third doses for those who received the Moderna vaccine, administration officials said Friday.

About nine out of 10 Brazilians have been vaccinated already or plan to be, according to pollster Datafolha. Most have gotten their first shot but not their second.

Brazil’s cases and deaths have been falling for two months, with 621 deaths reported in the seven days through Sept ember 2 — far below April’s peak of more than 3,000 reported deaths over a seven-day period. Older Brazilians have expressed concern about the efficacy of the Chinese Sinovac vaccine against the delta variant, prompting authorities to offer the booster shots.

Because of the variant, some experts say the government should slow the rollout of boosters and focus on distributing second doses. Delta is the most contagious variant identified, and many studies have suggested that one dose doesn’t protect against it. Two shots provide strong protection, with nearly all hospitalisations and deaths among the unvaccinated.

Ethel Maciel, an epidemiologist and professor at the Federal University of Espirito Santo, said pushing boosters at this early stage recalls the lack of concern given the gamma variant that overwhelmed Amazonian city Manaus earlier this year, only to feed a new wave nationwide. Brazil has seen more than 580,000 deaths from COVID-19, making it home to world’s eighth-highest toll on a per-capita basis.

“It seems we’re in the same movie, repeating the same errors,” Maciel said. “It’s only a matter of time until what’s happening in Rio leads to a greater number of more serious cases in the rest of the country.”

The delta variant already is dominant in Rio de Janeiro state, detected in 86 per cent of the samples collected from COVID-19 patients, according to the Ministry of Science, Technology and Innovation. Intensive care units have reached full capacity in eight municipalities, although only a small rise in deaths have been recorded so far.

Authorities in Sao Paulo state expect a similar scenario within weeks. It registered its first confirmed death from the delta variant on Tuesday, a 74-year-old woman who had received two Sinovac shots.

Globally, doubts have plagued Chinese vaccines, especially as the delta variant has gained hold in many countries. Chinese officials have maintained the vaccine protects against delta, particularly preventing hospitalisations and severe cases.

Still, Brazil’s Health Minister Marcelo Queiroga said August 25 that people aged 70 or older or who have a weak immune system will be eligible for a third dose, starting September 15 — preferably with the Pfizer vaccine. He said that people over 18 will have received their first doses by then, although he didn’t address their vulnerability to the delta variant without a second shot.

He also criticised governors and mayors who sought to deliver booster shots earlier, saying it could lead to vaccine shortages.