The focus should instead be on hospitalizations and deaths, said Ashish K. Jha, dean of Brown University's School of Public Health.

In an interview with ABC News on Sunday, Jha discussed the number of breakthrough COVID cases occurring in people who have been vaccinated and boosted. He noted that the Omicron variant is mutated and that "our antibodies just work a little bit less efficiently" against it.

"And so if you get a high enough dose of this virus, it'll break through that first wall of your immune system," Jha said. But the immune system in those who have been vaccinated has "a second wall" that prevents severe illness, he noted, pointing out that most people with breakthrough cases report mild symptoms.

ABC Host Jonathan Karl said that since the beginning of the pandemic, the number of COVID infections in the U.S. has "been the leading indicator of how bad things are getting, or how effectively we're dealing with the pandemic." He then asked, "Are we getting to the point where that indicator really isn't the one that matters? If new cases, as you said, among the vaccinated are not leading to serious sickness, is it an indicator that we should really be paying so much attention to?"