United States-based drugmaker Moderna on Tuesday announced it had started testing its coronavirus vaccine on children in a mid-to-late stage study. The company said the tests will help in understanding if the vaccine protected children from getting infected if they come into contact with the coronavirus.

The clinical trial, called the KidCOVE study, will enroll approximately 6,750 children in the US and Canada, aged six months and less than 12 years old. The vaccine has already been authorised for emergency use in the United States on those who are aged 18 and older.

The trial was broken into two parts, Moderna said, and different doses of the vaccine were being tested on children in the first part. Participants between the age of six months and one will receive two doses of the vaccine at an interval of about 28 days at either a 25 or a 50 or a 100 microgram level. Children between the ages of two and 11 will receive two doses of the vaccine spaced about 28 days apart at either a 50 or a 100 microgram level.

Follow-up of participants will be done through 12 months after the second vaccination. Based on this, Moderna will “evaluate the safety, tolerability, reactogenicity and effectiveness of two doses”, the company said.

The study is being conducted in collaboration with the National Institute of Allergy and Infectious Diseases at the National Institutes of Health, and the Biomedical Advanced Research and Development Authority at the US Department of Health and Human Services.

Moderna’s vaccine, which showed 94.5% efficacy during its phase three trials, is an mRNA vaccine. Messenger RNA vaccines use genetic instructions from the coronavirus to tell a person’s cells to make the spike protein. The vaccines must be shipped and stored at below–freezing or subzero temperatures and require a complicated cold chain to safely distribute them.