Brazil began vaccinating children aged five to 11 against Covid-19 on Friday after the move was approved, despite objections from President Jair Bolsonaro.
Davi Seremramiwe Xavante, an Indigenous eight-year-old boy, was the first child to be vaccinated during an official ceremony at a Sao Paulo hospital, with the state governor Joao Doria in attendance.
The first Covid vaccine dose administered in Brazil was also in Sao Paulo, in January 2021.
The new age group was approved for vaccination by Anvisa health authorities a month ago.
More than 20 million children are eligible for the Pfizer/BioNTech vaccine, as long as they have parental consent.
Indigenous people and children with health problems are priority groups for vaccination.
Bolsonaro has repeatedly criticized the move and has insisted he would never vaccinate his 11-year-old daughter, Laura.
Himself unvaccinated, Bolsonaro caused a storm when he asked to have the names of those responsible for approving the move made public.
An association representing Anvisa officials blasted Bolsonaro's "fascist methods," and the authority's president demanded police protection for staff following threats.
According to official health ministry figures, more than 300 children aged five to 11 have died from Covid-19 in Brazil, among a total of 620,000 deaths from the disease in the country of 213 million.
The number of new cases has exploded since the emergence of the Omicron variant in late November.
Daily new cases on Thursday were just under 100,000, having been less than 6,000 two weeks ago.
Friday, Brazil reported 112,286 new cases in 24 hours, a figure close to the record of 115,228 daily registered June 23, when the country was in the midst of the third wave of the pandemic.