Small doses of Pfizer’s COVID-19 mRNA in children ages 5 to 11 appeared to produce strong antibody responses and comparable side effects to those seen in older age groups, according to the first top-line results from a Phase 2/3 clinical trial released by Pfizer and its partner BioNTech early Monday.

The trial data involved 2,268 children ages 5 to 11 years, and these children were given a series of two 10-microgram doses of the vaccine, 21 days apart. The dosage is just a third of the 30-microgram doses given to people ages 12 and above.

One month after their second dose, researchers measured the children’s levels of antibodies able to neutralize SARS-CoV-2 virus in a lab experiment. The geometric mean titer of antibody in the 5 to 11 year olds was 1,197.6 (95 percent confidence interval of 1,106.1 to 1,296.6), which is comparable to the geometric mean titer of 1,146.5 seen in people ages 16 to 25.