It's a question of 'when, not if' the definition of fully vaccinated is changed to include a further shot, Fauci says

• Dr. Fauci said it was a matter of "when, not if" the definition of fully-vaccinated will change in the US.
• "I don't think anybody would argue that optimal protection is going to be with a third shot," Fauci told CNN.

Dr. Anthony Fauci, America's top medical doctor, said that it would be "a matter of when, not if," the definition of 'fully-vaccinated' is reclassified to include an additional shot.

His comments came after early stage lab studies suggested that a further dose of vaccine may be necessary to provide protection against the Omicron COVID-19 variant.

"I don't think anybody would argue that optimal protection is going to be with a third shot," Fauci, president Joe Biden's chief medical advisor, told CNN on Wednesday.

The definition of what constitutes fully-vaccinated could be important, particularly as some organisations require it of their employees.

Biden announced in September that the Department of Labor's Division of Occupational Safety and Health Administration would require large companies to ensure all their employees were fully vaccinated by January 4 or have them tested on a weekly basis and masked in the workplace.

An individual is currently considered 'fully-vaccinated' in the US two weeks after receiving a second dose of a two-dose COVID-19 vaccine – such as the Pfizer and Moderna shots – or two weeks after Johnson&Johnson's single dose shot, according to the Centers for Disease Control and Prevention.

Fauci told CNN that changing the definition was always "on the table" and was reviewed daily.

"It's a technical, almost semantic definition, and it is the definition for requirements," he said.

"My own personal opinion is that it is going to be a matter of when, not if," Fauci said.

The CDC recommends an extra booster dose of any authorized vaccine for every adult six months after a second dose of Moderna or Pfizer's vaccine, or two months after a J&J shot. For immunocompromized people, it's an additional shot 28 days after a second dose of either the Pfizer or Moderna vaccine, and then a booster shot six months after that. For immunocompromized Americans that received a J&J shot, it's just a booster 2 months later.

About 60% of the US population is fully vaccinated, under the current definition, and of that group, 24.4% have received a booster dose, CDC data show.

A series of very early lab studies released on Tuesday and Wednesday found that antibodies produced after two doses of Pfizer's COVID-19 vaccine may not bind so well to Omicron. Antibodies are just one part of the immune system and it's not yet clear exactly how much protection COVID-19 vaccines will provide against Omicron.

Peter Hotez, dean for the National School of Tropical Medicine at Baylor Medical, told CNN Wednesday that people who have had two doses of a COVID-19 shot will need a third. "We should think of the COVID-19 vaccine as a three dose vaccine," he said. Johnson&Johnson's single dose vaccine was not included in the lab tests.

Dr. Leana Wen, visiting professor of health policy and management at the George Washington University Milken Institute School of Public Health told CNN that she hoped federal health officials would "be quick to reevaluate the definition of what it means to be fully vaccinated, especially in light of what we're learning about Omicron."

But the practicalities of changing the definition could be a challenge.

Dr. William Schaffner, chair of the department of preventive medicine at Vanderbilt University School of Medicine and liaison to the CDC's Advisory Committee on Immunization Practices, told CNN Wednesday that changing the definition would be a "large leap".

"Changing the requirements of what fully vaccinated means, I think, has all kinds of downstream effects for all kinds of institutions in the country," he said. "I don't think we're quite there yet."