WASHINGTON — The nation’s top infectious disease expert is acknowledging “confusion” after the Centers for Disease Control and Prevention last week said fully vaccinated people don’t need to wear masks in most instances, even indoors.

Dr. Anthony Fauci tells ABC News, “The problem and the issue is that we don’t have any way of knowing who is vaccinated and who’s not vaccinated.”

He says it is “reasonable and understandable” that some businesses and localities are maintaining mask requirements because they can’t be sure of an individual’s vaccination history. But he says it’s important to note those measures protect the unvaccinated from each other, and vaccines provide a high level of protection for those who have gotten them.

Fauci says children who are not vaccinated — including children under 12 who won’t be eligible for vaccines for months — should continue to wear masks indoors. But he says that recommendation could change as the CDC conducts more research and more Americans get shots.