COVID-19 boosters: Fauci says definition of ‘fully vaccinated’ could change

Could the definition of "fully vaccinated" change now that boosters are available to all adults in the United States who are 18 or older? According to Dr. Anthony Fauci, it’s a possibility. 

The nation’s top infectious disease expert said the definition of being fully vaccinated, which is two doses of either the Moderna or Pfizer-BioNTech coronavirus vaccine or one dose of the Johnson & Johnson vaccine, could depend on how long immunity lasts in people following a booster dose. 

"We’re going to take a look right now at what the durability is of the booster. We’re going to follow people who get boosted," Fauci said during an interview on CNN’s "State of the Union" on Nov. 21. "We don’t know right now, you have to be perfectly transparent and honest. We’re going to be doing the best we can to keep the American public optimally protected. If that means that that’s going to be a boost that absolutely everyone will have to have, then so be it, we’ll do it that way, but it will be guided by the science. And people should not be put off by the fact that as time goes by, and we learn more and more about the protection, then we might modify the guidelines. That’s what we’ve been saying all along by ‘follow the science.’ Things change, you have to follow the data." 

For now, the definition of fully vaccinated will remain as two shots of a Pfizer or Moderna regimen or one shot of a J&J vaccine. 

"Well, two shots, for a time frame, means you are fully vaccinated," Fauci continued. "But the thing that you want to get the people, the viewers, to understand, it isn’t the effectiveness of the vaccine, it’s quite effective, it’s how long it lasts. And that’s the reason, when we started to see the immunity start to wane, we said people should get boosted. And that’s the reason why we’re going to keep following it closely." 

The U.S. last week opened COVID-19 booster shots to all adults and took the extra step of urging people 50 and older to seek one, aiming to ward off a winter surge as coronavirus cases rise even before millions of Americans travel for the holidays. 

Until now, Americans faced a confusing list of who was eligible for a booster that varied by age, their health and which kind of vaccine they got first. The Food and Drug Administration authorized changes to Pfizer and Moderna boosters to make it easier. 

Under the new rules, anyone 18 or older can choose either a Pfizer or Moderna booster six months after their last dose. For anyone who got the single-dose Johnson & Johnson vaccine, the wait already was just two months. And people can mix-and-match boosters from any company. 

"We heard loud and clear that people needed something simpler — and this, I think, is simple," FDA vaccine chief Dr. Peter Marks told The Associated Press. 

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The Centers for Disease Control and Prevention had to agree before the new policy became official late Friday. CDC Director Dr. Rochelle Walensky endorsed a recommendation from her agency's scientific advisers that — in addition to offering all adults a booster — had stressed that people 50 and older should be urged to get one. 

The CDC also put out a plea for those who had previously qualified but hadn't yet signed up for a booster to quit putting it off — saying older Americans and people with risks such as obesity, diabetes or other health problems should try to get one before the holidays. 

The expansion makes tens of millions more Americans eligible for an extra dose of protection. 

The No. 1 priority for the U.S., and the world, still is to get more unvaccinated people their first doses. All three COVID-19 vaccines used in the U.S. continue to offer strong protection against severe illness, including hospitalization and death, without a booster. 

FILE - Dosage of Moderna Covid-19 vaccine are being prepared to give to patients. (Francine Orr / Los Angeles Times via Getty Images)

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But protection against infection can wane with time, and the U.S. and many countries in Europe also are grappling with how widely to recommend boosters as they fight a winter wave of new cases. In the U.S., COVID-19 diagnoses have climbed steadily over the last three weeks, especially in states where colder weather already has driven people indoors. 

And about a dozen states didn't wait for federal officials to act before opening boosters to all adults. 

The Biden administration had originally planned on boosters for all adults but until now, U.S. health authorities — backed by their scientific advisers — had questioned the need for such a widespread campaign. Instead, they first endorsed Pfizer or Moderna boosters only for vulnerable groups such as older Americans or those at high risk of COVID-19 because of health problems, their jobs or their living conditions. 

This time around, the experts agreed the overall benefits of added protection from a third dose for any adult — six months after their last shot — outweighed risks of rare side effects from Moderna's or Pfizer's vaccine, such as a type of heart inflammation seen mostly in young men. 

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Several other countries have discouraged use of the Moderna vaccine in young people because of that concern, citing data suggesting the rare side effect may occur slightly more with that vaccine than its competitor. 

Pfizer told CDC's advisers that in a booster study of 10,000 people as young as 16, there were no more serious side effects from a third vaccine dose than earlier ones. That study found a booster restored protection against symptomatic infections to about 95% even while the extra-contagious delta variant was surging. 

Britain recently released real-world data showing the same jump in protection once it began offering boosters to middle-aged and older adults, and Israel has credited widespread boosters for helping to beat back another wave of the virus. 

While the vaccines spur immune memory that protects against severe disease, protection against infection depends on levels of virus-fighting antibodies that wane with time. No one yet knows how long antibody levels will stay high after a booster. 

The Associated Press contributed to this report.