Moderna (MRNA  ) announced on Tuesday that the first participants have received their doses of its new Phase 2/3 study of its coronavirus vaccine candidate, mRNA-1273, in children between the ages of 6 months to less than 12 years old.

The study, called the KidCOVE study, intends to enroll about 6,750 healthy children in the United States and Canada, testing the effectiveness and safety profile of the biotech's messenger RNA (mRNA) vaccine in the youngest populations.

Each participant in the expanded two-part study will receive two doses, 28 days apart. In the first part, children between the ages of 2 to less than 12 may receive two doses of either 50 or 100 micrograms of mRNA-1273 each. Those under 2 years may receive one of three dose levels of 25, 50 or 100 micrograms. An adult dose of mRNA-1273 is 100 micrograms.

In each age group, the first participants will receive the lowest dose level and be monitored for adverse reactions before later participants are given higher doses. From there, researchers will conduct an interim analysis to determine which dosing level will be used in the second part of the study, which is the placebo-controlled portion of the study.

Participants will be followed for one year after they receive their second dose, with researchers watching for side effects as well as potential coronavirus infections and developed antibody levels.

Moderna is also conducting a separate Phase 2/3 study with adolescents aged 12 to less than 18 which began dosing healthy participants back in December. The company intends to enroll 3,000 participants in the United States, with each receiving either 100 micrograms of mRNA-1273 or an inert placebo.

Currently, Moderna's vaccine is authorized for emergency use by the U.S. Food and Drug Administration in adults aged 18 years or older.

Rival vaccine developed by Pfizer (PFE  )-BioNTech (BNTX  ), which is authorized by the federal regulator for people as young as 16, is also conducting an expansion study on adolescents between the ages of 12 to 15. The study had fully enrolled 2,259 participants in January, according to CNBC.

AstraZeneca (AZN  )-Oxford has also started trials on children between the ages of 6 to 17 years, planning to enroll 300 volunteers.

"While most children are relatively unaffected by coronavirus and are unlikely to become unwell with the infection, it is important to establish the safety and immune response to the vaccine in children and young people as some children may benefit from vaccination," said Dr. Andrew Pollard, chief investigator on the Oxford vaccine trial, in a statement. "These new trials will extend our understanding of control of SARS-CoV-2 to younger age groups."