The U.S. FDA recommended a 10 mcg dose of the Pfizer vaccine for use in children 5 to 11 years old - one third of the 30 mcg dose used for people 12 and older. Clinical trial data showed that a smaller dose for children 5 to 11 produces a strong immune response (very similar to that of adults with a 30 mcg dose) and causes fewer side effects than a 30 mcg dose.