CNBC host confronts Dr. Fauci about breakthrough cases and why the CDC no longer tracks them

A CNBC host confronted Dr. Anthony Fauci recently about the frequency of so-called "breakthrough" COVID-19 cases in people who are fully vaccinated.

What is the background?

Public health officials have been touting the efficacy of the COVID-19 vaccines for nearly a year now — and for good reason. The vaccines are more effective than first believed, especially considering scientists developed the vaccine less than one year after sequencing COVID-19's genetic code.

But with governments pushing vaccine mandates, breakthrough cases — in which a fully vaccinated person contracts COVID-19 — seem to be increasingly frequent. So that begs the question: How can you force people to get vaccinated if a significant number of people are contracting COVID despite being fully vaccinated?

The exact number of breakthrough cases, in fact, is not even known. The Centers for Disease Control and Prevention stopped tracking that data in May. The agency has continued, however, to track hospitalizations and deaths among the fully vaccinated crowd. As of Sept. 27, the CDC reported "22,115 patients with COVID-19 vaccine breakthrough infection who were hospitalized or died."

What happened?

During an interview on "Closing Bell" Friday, host Sara Eisen confronted Fauci about breakthrough cases, asking him if the government is being "too casual about the limitations of the vaccine."

Eisen was asking because she contracted COVID-19 despite being fully vaccinated. She said the virus had recently spread through her "entire family."

In response, Fauci cited data that say unvaccinated people still remain most vulnerable to hospitalization or death from COVID, and the vaccination protects most people from a severe outcome if they contract COVID-19. Fauci told Eisen she should not "confuse" the "overwhelming benefits of the protection of vaccines" with occurrences of breakthrough cases.

But Eisen pushed back. Noting the CDC no longer tracks breakthrough cases, Eisen asked Fauci directly: "How do we know that [breakthrough cases are] happening to a small proportion and how do we know that they are tending to be mild?"

Fauci, however, did not directly answer the question, instead promoting booster shots before contradicting what the CDC has said about how readily vaccinated people transmit COVID-19.

So, in answer to your very appropriate question about if you get vaccinated and you get infected, is there less of a chance that you will be transmitting it to someone who is unvaccinated or someone who is vulnerable? The chances of doing that are diminished by being vaccinated and even further diminished, according to preliminary data we'll wait to see the real fundamental core of the data, but it looks like that extra added of protection from a boost will be very valuable.

What has the CDC said?

Contrary to what Fauci said, the CDC has not said the chances of people transmitting COVID-19 have "diminished" if you are fully vaccinated. In fact, the CDC says that fully vaccinated people can transmit the virus as readily as unvaccinated people.

Current CDC information states that viral load of the Delta variant is similar for vaccinated people and unvaccinated people — meaning both are similarly contagious. The agency, however, says vaccinated people are contagious for less time than unvaccinated people.

"For people infected with the Delta variant, similar amounts of viral genetic material have been found among both unvaccinated and fully vaccinated people. However, like prior variants, the amount of viral genetic material may go down faster in fully vaccinated people when compared to unvaccinated people," the CDC explains. "This means fully vaccinated people will likely spread the virus for less time than unvaccinated people."