BOSTON (CBS) - Johnson & Johnson is now testing its COVID-19 vaccine on teenagers.

The company announced Friday it's testing the vaccine in a "small number" of kids ages 16 and 17. The study will then be expanded to a larger group of children as young as 12.

This trial is currently enrolling participants in Spain and the United Kingdom and will begin soon in the U.S.

Johnson & Johnson's single-shot vaccine is currently approved for emergency use in the U.S. for anyone 18 and older.

Pfizer said on Wednesday its two-dose vaccine is 100-percent effective in kids ages 12 to 15. It's vaccine is approved for emergency use in anyone age 16 or older.

Earlier this month, Cambridge-based Moderna started a study of its coronavirus vaccine in children under the age of 12.