While speaking at a Wednesday CDC briefing, Fauci said that the decision over a fourth dose would depend on data collected after the third dose.

"You measure laboratory phenomenon, but you measure the real-world data on the efficacy in preventing, for example, hospital visits as well as hospitalizations," he said. "And I believe that you're going to be hearing data about that as the data become available."

Meanwhile, Fauci told the Financial Times that there's no way to fully eliminate Covid-19, but that the United States is past the "full-blown" Covid-19 pandemic phase.

"We are looking at a time when we have enough people vaccinated and enough people with protection from previous infection that the COVID restrictions will soon be a thing of the past," he said.