Dr. Anthony Fauci defended comments he made last week when he based the percentage of the population that needed to be vaccinated in order to reach herd immunity on public polling.

“We have to realize that we have to be humble and realize what we don’t know,” Fauci said on CNN’s State of the Union. “These are pure estimates, and the calculations that I made — 70%, 75% — it’s a range. The range is going to be somewhere between 70% and 85%.”