MEXICO CITY, Mexico -- Mexico on Monday began COVID-19 vaccinations for adolescents with chronic diseases in the capital, the latest step in an immunization drive in one of the countries hit hardest by the pandemic.

Authorities in Mexico City said they had begun using the Pfizer-BioNTech vaccine to inoculate minors with comorbidities aged between 12 and 17 years old.

Fifteen-year-old Paola Abigail Chocooj, who has diabetes, was among those participating, some in their school uniforms.

Her mother Ileana Silva said she had been "very nervous" since the pandemic started that her daughter would be infected, but was now feeling "a little bit calmer."

The northwestern state of Baja California, bordering the United States, also began Covid-19 vaccinations for minors with serious illnesses.

The Mexican government did not include minors in its national immunization plan, saying that exposing them at an early age to the vaccine could affect their immune systems.

However, a court ruled this month the policy must be changed so that minors aged 12-17 are widely immunized -- a verdict the government said it is analyzing.

Around 25 million school students returned to classrooms at the end of August, and some parents have taken legal action to have their children vaccinated.

The country of 126 million people has an official Covid-19 death toll of more than 286,000, the world's fourth highest.

Around 53.5 million adults have been fully vaccinated in Mexico.

Elsewhere in the region, Nicaragua on Monday began immunizing children from the age of two with Covid-19 vaccines developed by Cuba.

Authorities in the Central American nation said they plan voluntarily vaccinations for some 2.1 million children and adolescents.