The US has approved Pfizer's COVID-19 vaccine for children as young as 12

Pfizer's COVID-19 vaccine has become the first to be approved in the US for children aged 12 to 15 after regulators altered its emergency use authorisation.

Katelyn Evans, a participant in a clinical trial of Pfizer's COVID-19 vaccine, gets her shot at Cincinnati Children’s Hospital Medical Center in October, 2020. Source: Cincinnati Childrens Hospital Medical Center

US regulators have authorised Pfizer and BioNTech's COVID-19 vaccine for use in children as young as 12, widening the country's inoculation program as vaccination rates have slowed significantly.

The vaccine has been available under an emergency use authorisation to people as young as 16 in the United States.

The vaccine makers said they had started the process for full approval for those ages last week.

The US Food and Drug Administration said it was amending the EUA to include the millions of children aged 12 to 15.

It's the first COVID-19 vaccine to be authorised in the United States for this age group, seen as an important step for getting children back into schools safely.

US President Joe Biden has asked states to make the vaccine available to the younger adolescents immediately.

Most children with COVID-19 only develop mild symptoms or no symptoms at all.

However, children are not without risk of becoming seriously ill, and they can still spread the virus. There have been outbreaks traced to sporting events and other activities for children in this age range.

Pfizer and BioNTech asked the FDA to expand their EUA to include the younger age group in early April.

Nearly 46 per cent of people in the United States had received at least one shot of a COVID-19 vaccine as of Sunday, according to data from the US Centers for Disease Control and Prevention.

But the pace of US vaccinations has slowed significantly since topping out at a seven-day average of more than 3.3 million doses a day in mid-April.

That average had fallen by more than a third to about 2.1 million shots a day as of 4 May.

Pfizer's vaccine is the only one authorised for 16 and 17-year-olds in the United States.

Nearly two million people in that age group have received at least one shot, according to CDC data.

Widely vaccinating 12- to 18-year olds could allow US schools to relax masking and social distancing measures suggested by the CDC.

Pfizer expects to have safety and efficacy data for children ages two to 11 in September, when it plans to ask for further expansion of the EUA for that age group.