The nation’s top infectious disease official says a vaccine for children under the age of 5 may take another month.

Dr. Anthony Fauci of the National Institutes of Allergy and Infectious Diseases says he has hopes that a vaccine for preschool-aged children might be ready within a month, but might take a little longer. He says the FDA will establish the actual timeline.

Fauci says Pfizer’s dose for children age 6 months to 2 years is showing a good response, but isn’t the case for children between 2 and 4 years of age.

Pfizer is continuing to establish the correct dose before turning their data over to the FDA.