U.S. health officials said on Wednesday that they have not changed their eligibility for “full vaccination” against COVID-19, but they urge Americans to “know in time” their protection against the virus through booster vaccination if they qualify.

Maintaining the current definition of full vaccination—either a two-dose mRNA vaccine from Pfizer and Moderna, or a single-dose vaccine from Johnson & Johnson—while health officials warned that the protective effect of the initial dose would be weakened. They encourage Americans to receive additional doses to avoid serious illness and death due to delta and omicron variants.

The decision to retain the original definition established when the vaccine was first introduced more than a year ago means that vaccination requirements for federal travel or employment do not require booster doses.

Maintaining the current definition of “fully vaccinated” may make it more difficult to encourage some Americans who reluctantly get the first dose of the vaccine to boost their vaccination because they will not face the onerous restrictions that are often imposed on unvaccinated people— Including testing requirements or, in some jurisdictions, prohibiting access to indoor dining and other facilities.

Dr. Rochelle Varensky, director of the Centers for Disease Control and Prevention, said: “If individuals receive the main series of vaccines, they are considered to have been fully vaccinated against COVID-19.” “This definition will not change.”

Instead, the CDC releases information for Americans to more easily determine whether they are eligible for a booster dose in order to keep up with their COVID-19 vaccine.

“We now recommend that individuals stay informed about the additional doses they are eligible for,” Varensky added.

Similarly, Jeff Zients, the White House COVID-19 coordinator, stated that the government has not considered making adjustments to require international travel or President Joe Biden’s actions to pressure tens of millions of Americans. Workers covered by a series of vaccination tasks get shots by injecting booster needles.

“This hasn’t changed, and we don’t have any plans to change,” he told reporters at the White House briefing.

According to data from the Centers for Disease Control and Prevention, more than 71 million Americans received the booster dose.

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Zients said: “I do think it is very important to recognize that the vast majority of hospitalizations and deaths occur in unvaccinated Americans.” “Completing the primary vaccination series is clearly a key step in preventing serious consequences, just as Dr. Wallensky said that booster vaccines provide the highest level of protection.”

He added: “As for the definition, if someone has been vaccinated with the main series of vaccines, it is considered to be fully vaccinated.”

On Wednesday, shortly before the White House briefing, the CDC revised an agency website called “When you are fully vaccinated,” which defines the term and discusses what people can do after reaching this level of protection .

It was renamed “Keep up-to-date vaccines” and the term “fully vaccinated” was used carefully to describe the main series. Most of the content on this website discusses additional doses and booster doses.

When asked about this change, a CDC spokeswoman said that the definition of “fully vaccinated” has not changed. But she also said: “The CDC will now use the term’up to date’ when talking about COVID-19 vaccination. Based on CDC recommendations, the CDC recommends that individuals stay’up to date’ by receiving any additional doses they are eligible for,” To ensure they have the best protection against COVID-19. “

Dr. Anthony Fauci, Biden’s chief scientific adviser to COVID-19, said on Tuesday that the government is changing the way it talks about vaccination and booster doses.

He said in a speech at the National Institutes of Health: “The term we use now is’keep your vaccination up to date’, not’fully vaccinate’.”