WASHINGTON, United States (AFP)— Pfizer said Thursday it had begun clinical trials for its COVID vaccine in children under the age of eleven, an early sign of the next stage of the global immunization campaign.

“Together with our partner BioNTech, we have dosed the first healthy children in a global Phase 1/2/3 continuous study to further evaluate the safety, tolerability, and immunogenicity of the Pfizer-BioNTech COVID-19 vaccine,” the company said in a statement to AFP.

“We are proud to start this much needed study for children and families eagerly awaiting a possible vaccine option.”

According to details posted on the site clinicaltrials.gov, the company is testing three different dosing levels for use in this age group. 

The company is already testing the shots in children aged 12 to 15, and its US emergency authorization covers people aged 16 and up. 

Pfizer joins Moderna and AstraZeneca in testing their vaccines in younger children, while Johnson & Johnson has plans to follow.

While children are generally spared the worst of the disease and are less likely than adults to transmit the virus, rare cases of serious COVID and deaths do occur, as well as a post-infectious inflammatory condition called MIS-C.

Under-18s account for roughly a fifth of the US population of 330 million, and most experts believe it will be necessary to make inroads towards immunizing children in order to achieve population level immunity.