CDC on Wednesday said it was not changing its original definition of "fully vaccinated." Instead, the agency recommends individuals be "up to date" with their Covid-19 vaccines by receiving a booster dose when eligible.

Some experts have advocated for changing the definition of 'fully vaccinated'

After booster doses of the Covid-19 vaccines were made available to a broader population in November, some state officials and health experts advocated for changing the definition of "fully vaccinated" to include the additional dose.

For example, Connecticut Gov. Ned Lamont (D) and New Mexico Gov. Michelle Lujan Grisham (D) have both previously expressed interest in changing the definition of fully vaccinated in their states to include booster doses.

Separately Peter Hotez, dean for the National School of Tropical Medicine at the Baylor College of Medicine said that people should "think of the Covid-19 vaccine as a three-dose vaccine."

Similarly, Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, in December said he believed it was "going to be a matter of when, not if" the definition of fully vaccinated would change. "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 dose," Fauci said.

CDC keeps definition of 'fully vaccinated,' encourages being 'up to date' instead

However, CDC on Wednesday said that it was not changing its definition of fully vaccinated.

"The technical definition of 'fully vaccinated'—two doses of an mRNA vaccine or one dose of the [Johnson & Johnson (J&J)] vaccine—has not changed," said Kristen Nordlund, a CDC spokesperson. "Individuals are considered fully vaccinated once they have received their primary series."

Instead, CDC recommended Americans remain "up to date" on their Covid-19 vaccines. To be considered "up to date" with Covid-19 vaccination, the agency said Pfizer-BioNTech and Moderna recipients should receive three doses of a vaccine, and J&J recipients should receive two doses, preferably with the second being an mRNA vaccine. According to CDC data, more than 71 million Americans have already received a booster dose.

"Consistent with how public health has historically viewed or even talked about how we recommend vaccines, we are now recommending that individuals stay up to date with additional doses that they are eligible for," said CDC Director Rochelle Walensky.

According to Nordlund, CDC's changed recommendations for the Covid-19 vaccines were made to "align with standard language CDC uses about other vaccinations." She added that the new recommendations account for differences in booster eligibility, whether due to age or insufficient length of time after a primary series.

"CDC will now use the phrase 'up to date' when talking about Covid-19 vaccination," Nordlund said. "CDC recommends that individuals stay 'up to date' by receiving any additional doses they are eligible for, according to CDC's recommendations, to ensure they have optimal protection against Covid-19."

In addition, the decision to keep the original definition of fully vaccinated in place means that people will not be required to receive an additional dose to comply with any federal vaccination requirements for travel or employment, USA Today reports.

"If you think about the different requirements [for federal vaccine mandates], that has not changed, and we do not have any plans to change that," said Jeffrey Zients, the White House Covid-19 response coordinator.

"I do think it's really important to recognize the vast majority of hospitalizations and deaths are among the unvaccinated Americans," Zients added. "Completing the primary vaccination series is clearly a critical step to prevent severe outcomes, with boosters ... giving the highest level of protection." (Weiland/Anthes, New York Times, 1/5; Bacon et al., USA Today, 1/6; AP/Modern Healthcare, 1/5)