case total of 28.1 million is an undercount, Gottlieb told CNBC he believes about 120 million people — or roughly 36% of the American population — has been infected with the coronavirus throughout the pandemic.

"When you're getting to 40% or 50% of the population with some form of protective immunity, you don't have herd immunity but you have enough immunity in the population that this [virus] just doesn't transfer as readily," Gottlieb said.

"I do think that as we get into the warm weather, as we vaccinate more of the population and in view of the fact that at least one-third of Americans have had this, I do think that infection levels are going to come down dramatically over the course of the spring and summer," Gottlieb said.

Anthony Fauci has previously said that 75% to 85% of the population would need to develop immunity to create an "umbrella" of protection.

Officials with the CDC also recently said that upward of 85% of people would need to be covered to achieve so-called herd immunity if a fast-spreading virus variant, such as B117, which was first reported in the U.K., become the dominant strain in the U.S.

"I think people are going to be going out and doing a lot of stuff this summer, a lot of pent-up demand for consumer spending," he said.

"I think in the fall we're going to have to take certain precautions, but we're going to be back doing stuff.