March 16 (UPI) -- Drug maker Moderna announced plans Tuesday to start new clinical trials of its COVID-19 vaccine in children ages 6 months to 12 years.
Some children who are participants in the two-part, Phase 2/3 trial of the company's mRNA-1273 vaccine already received their first doses as patient enrollment continues, company officials said.
The trial will assess the safety and effectiveness of the vaccine in infants and children and seek to identify the dosing level that provides the most protection against the virus with the fewest side effects, they said.
"We are pleased to begin this Phase 2/3 study of mRNA-1273 in healthy children in the U.S. and Canada," Moderna CEO Stéphane Bancel said in a statement.
"We are encouraged by the primary analysis of the Phase 3 COVE study of mRNA-1273 in adults ages 18 and above and this pediatric study will help us assess the potential safety and [effectiveness] ... in this important younger age population," he said.
Drugs and vaccines must complete three phases of clinical trials before they can be approved for use.
The Moderna vaccine is one of three currently approved for use in the United States, along with shots from Pfizer-BioNTech and Johnson & Johnson.
The two-dose vaccine received an emergency use authorization from the U.S. Food and Drug Administration in December, clearing it for adults age 18 years and older.
The Johnson & Johnson vaccine is also only approved for adults, while the Pfizer shot can be used in those age 16 and older.
Adults were given priority in the initial trials of the vaccines as children are at lower risk for serious illness from COVID-19.
However, children who do get seriously ill from the virus can develop significant health complications, similar to Kawasaki disease, research suggests.
The Phase 2/3 study, called the KidCOVE, is being conducted in collaboration with the National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health and the Biomedical Advanced Research and Development Authority, Moderna officials said.
In the first part of the study, each participant age 2 to 12 may receive one of two dose levels of the vaccine, while those age 6 months to 2 years may receive one of three, lower, dose levels.
The best-performing dose level in terms of safety and effectiveness will be used in the second part of the study, and participants will be followed for 12 months after the second vaccination.
Pfizer-BioNTech began studying its two-dose vaccine in children ages 12 to 15 in late January, and more than 1,200 participants have been enrolled in a trial.
The company also announced plans to study the safety and effectiveness of the vaccine in children ages 5 to 12 in a new trial this summer.