WASHINGTON (AP) — U.S. health officials said Wednesday they are not changing the qualifications for being "fully vaccinated" against COVID-19, but they are urging Americans to stay "up to date" on their protection against the virus by getting booster shots when eligible.

The move to keep the existing definition of fully vaccinated — either two doses of the mRNA vaccines from Pfizer and Moderna or a single dose of the Johnson & Johnson vaccine — comes as health officials warned of waning protections from the initial doses. They are encouraging Americans to get additional doses to stave off serious illness and death from the delta and omicron variants.

The decision to keep the initial definition, established more than a year ago when the vaccines first rolled out, means that federal vaccination mandates for travel or employment won't require a booster dose.

Maintaining the existing definition of "fully vaccinated" could make it more difficult to encourage some Americans who only begrudgingly got their primary doses of the vaccine to get boosted, since they would not face onerous restrictions often imposed on the unvaccinated — including testing requirements or, in some jurisdictions, being barred from indoor dining and other facilities.

"Individuals are considered fully vaccinated against COVID-19 if they've received their primary series," said Centers for Disease Control and Prevention Director Dr. Rochelle Walensky. "That definition is not changing."

The CDC instead posted information for Americans to more easily determine their eligibility for booster doses so as to remain up to date with their COVID-19 shots.

"We are now recommending that individuals stay up to date with additional doses that they are eligible for," Walensky added.

Similarly, Jeff Zients, the White House COVID-19 coordinator, said the administration was not considering an adjustment to require booster shots for international travel or for workers covered by a slew of vaccination mandates instituted by President Joe Biden to press tens of millions of Americans to get the shots.

"That has not changed and we do not have any plans to change that," he told reporters during a White House briefing.

More than 71 million Americans have received a booster dose, according to CDC data.

"I do think it's really important to recognize the vast majority of hospitalizations and deaths are among the unvaccinated Americans," Zients said. "Completing the primary vaccination series is clearly a critical step to prevent severe outcomes, with boosters as Dr. Walensky said, giving the highest level of protection."

He added, "As to the definition, someone is considered fully vaccinated if they've received their primary series of vaccine."

On Wednesday, shortly before the White House briefing, the CDC revised an agency web site that had been entitled "When You've Been Fully Vaccinated" that defined the term and talked about what people could do after they achieved that level of protection.

It was retitled "Stay Up to Date with Vaccines," and used the term "fully vaccinated" sparingly, to describe the primary series. Much of the site discussed additional and booster doses.

Asked about the change, a CDC spokeswoman said the definition of "fully vaccinated" has not changed. But she also said: "CDC will now use the phrase 'up to date' when talking about COVID-19 vaccination. 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."

Dr. Anthony Fauci, Biden's top science adviser on the COVID-19 response, said Tuesday that the administration was shifting how it talked about vaccinations and getting booster doses.

"We're using the terminology now 'keeping your vaccinations up to date,' rather than what 'fully vaccinated' means," he said during a National Institutes of Health lecture.

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Stobbe reported from New York.