Fauci: It's 'when, not if' definition of fully vaccinated will change

Anthony Fauci said Wednesday he thinks the definition of being fully vaccinated will eventually change to include a booster, especially as new evidence is emerging that a booster dose offers the best protection against the omicron variant.

"Right now, I don't see that changing tomorrow or next week," Fauci, the nation's top infectious diseases expert, said in an interview with CNN's Kate Bolduan.

But he added that his "own personal opinion" is that "it's going to be a matter of when, not if."

Still, Fauci noted that the definition of what it means to be fully vaccinated is a matter of semantics. What matters is the emerging evidence that a booster dose offers more protection than the initial series.

"Certainly, when you want to talk about what optimal protection is, I don't think anybody would argue that optimal protection is going to be with a third shot," Fauci said.

Fauci's comments came shortly after Pfizer and BioNTech said preliminary data showed that the newly discovered omicron variant was partially able to escape the antibodies found in people with two shots of the vaccine, leaving them vulnerable to infection.

The company data, which was announced in a press release and not peer reviewed, showed a booster shot raised the levels of neutralizing antibodies high enough to block the variant, meaning the additional dose would add more protection against milder infections caused by omicron.

A debate has emerged around what it means to be fully vaccinated against COVID-19 as some state and local officials have been pushing to change the definition to include an additional dose.

But some infectious disease experts argue that antibodies are not the only way to measure a vaccine's performance, and people with two doses of an mRNA vaccine are still likely protected against severe disease and hospitalization.