U.S. health officials are mulling over whether they should change the definition of "fully vaccinated" against COVID to mean that a person has gotten two shots and a third booster shot of the vaccine. Now that the Centers for Disease Control (CDC) and the Food and Drug Administration (FDA) has approved COVID vaccine booster shots, CDC Director Dr. Rochelle Walensky hinted that the agency "may need to update" what it means to be fully vaccinated.

"We have not yet changed the definition of 'fully vaccinated.' We will continue to look at this," Dr. Walensky said during a White House briefing on Friday, as reported by CBN News. "We may need to update our definition of 'fully vaccinated' in the future."

Currently, the CDC defines "fully vaccinated persons" as "those who are 14 or more days post-completion of the primary series of an FDA-authorized COVID-19 vaccine." Dr. Walensky reminded the qualified public to get a booster shot. She said, "If you're eligible for a booster, go ahead and get your booster."

According to latest CDC data, the U.S. has fully vaccinated 190.6 million people aged 12 and above, while 12.9 million people have received a booster dose. This makes 96.3% of people aged 65 and older fully vaccinated with a booster dose. 79.5% or 205.2 million people aged 18 and above are fully vaccinated with a booster dose and 77.6% if accounting for those aged 12 and above.

According to the Washington Post, the CDC on Thursday endorsed recommendations from expert advisers for "endorsed recommendations from expert advisers for mixing and matching of coronavirus vaccines for booster shots, as they unanimously recommended additional doses of Moderna and Johnson & Johnson's shots" for Americans across the country. The panel recommended that those who are eligible to get boosters may choose from any of the Pfizer, Moderna, or Johnson & Johnson's vaccines no matter what the brand of their first shots were.

Mixing and matching, more properly known as cross inoculation, has shown to increase antibody levels, specifically among those who received the Johnson & Johnson COVID vaccine, AARP reported. Preliminary results from a National Institutes of Health (NIH) study found that those who had the one-shot J&J vaccine and got a J&J booster demonstrated a fourfold increase in antibody levels in just 15 days. Those who first received a J&J shot then a Moderna shot showed a 76-fold increase of antibody levels. Those who got a J&J shot and then a Pfizer booster shot showed a 35-fold increase in antibody levels.

While mixing and matching or cross inoculation is not commonly done with other vaccines, infectious disease expert Dr. Monica Gandhi, who is also a professor of medicine at University of California, San Francisco said that it's "pretty new" to have "multiple vaccines available for a pandemic."

Earlier this month, White House medical advisor Dr. Anthony Fauci signaled wanting to redefine what it means to be "fully vaccinated" against COVID. He said, "I believe that a third-shot booster for a two-dose mRNA [vaccine] should ultimately and will ultimately be the proper, complete regimen."