The delay means parents hoping to get younger kids vaccinated will have to wait a little longer.
The data is expected to be available in early April, the companies said.
It was originally scheduled for Feb. 15.
Children age 5 and upare already eligible for a COVID-19 vaccine.
This prompted the company to start testing a three-dose version of the vaccine for children under age 5.
The vaccine for kids ages 5 to 11 is one-third the adult size.
CNET’s Jessica Rendall contributed to this report.