Moderna announced Tuesday that it has begun testing its COVID-19 vaccine on children 6 months to 11 years old.

The drugmaker is the first U.S. company to test its vaccine on infants and young children. 

The two-part clinical trial will enroll approximately 6,750 children in the United States and Canada. Moderna said the first participants have already been dosed. 

“We are pleased to begin this Phase 2/3 study of [the vaccine] in healthy children in the U.S. and Canada … ,” Moderna CEO Stéphane Bancel said in a news release. “This pediatric study will help us assess the potential safety and immunogenicity of our COVID-19 vaccine candidate in this important younger age population.”

Part 1 of the study experiments with different dose levels. Participants ages 2 to 11 will either be given 50 or 100 micrograms, while children 6 months to 2 years old will be given either 25, 50 or 100 micrograms. 

After analyzing the Part 1 data, Moderna will determine which dosage will be used in Part 2, which will be placebo-controlled. 

Participants will be monitored for 12 months after receiving the second dose of the two-shot vaccine, although, if the vaccine is successful, a request for emergency use authorization from the Food and Drug Administration would likely come much sooner. 

Moderna did not provide an estimated timeline for when its vaccine might be available to children in the general public.

The study is being conducted in collaboration with the National Institute of Allergy and Infectious Diseases and the Biomedical Advanced Research and Development Authority. 

Moderna, with the help of the National Institues of Health, has developed one of three coronavirus vaccines currently approved for emergency use in the U.S. In adults, preliminary clinical trial data showed that the vaccine was safe and 94.5% effective at preventing COVID-19. 

The vaccine is approved for people age 18 or older. The company is separately testing it in 12- to 17-year-olds.

Pfizer is testing its vaccine in children 12 to 15 years old — it is currently authorized for 16 and older. 

Johnson & Johnson said last month it will begin testing its vaccine in kids 12 to 17 and then move down in age from there. CEO Alex Gorsky said it’s likely the company will have a pediatric vaccine available by September.

Correction: This article previously said the new testing would be conducted on children ages 6 months to 12 years old. Moderna's announcement said the testing would include "children ages 6 months to less than 12 years."