Dr. Anthony Fauci clarified Thursday that whether a Covid-19 vaccine booster shot will be needed in the next year remains an open question.
"The bottom line is, we don't know if or when we will need booster shots," Fauci, director of the National Institute of Allergy and Infectious Diseases, told NBC News. "But it would be foolish not to prepare for the eventuality that we might need it."
During an Axios event Wednesday that also featured Pfizer CEO Albert Bourla, Fauci said "I think we will almost certainly require a booster sometime within a year or so after getting the primary [shot] because the durability of protection against coronaviruses is generally not lifelong."
The Covid-19 vaccines have so far proven to be extremely good at preventing people from getting sick — even if they do become infected.
"We're seeing a very, very high degree of effectiveness," Fauci said. "To me, that's a strong endorsement of why more people should be getting vaccinated."
One question now is how long that protection lasts. Pfizer's clinical trials have suggested its vaccine is safe and offers high levels of protection for at least six months after the second dose. Studies are ongoing to determine how much longer that effectiveness lasts, with results expected within the coming months.
Indeed, drugmakers are working under the assumption that an additional dose will be needed.
"Until we see a reduction in SARS-CoV-2 circulation and Covid-19 disease, we think it is likely that a third dose, a boost of our vaccine, within 12 months after vaccine administration, will likely be needed to help provide protection," a Pfizer spokesperson said in an emailed statement. "We are also prepared to update the vaccine quickly should variants emerge that escape current vaccine protection."
Moderna, too, is studying both a third dose of its vaccine and a tweaked version meant to target certain variants.
It's unclear which type of booster — an identical shot or a modified version — would be needed in the future, and how long after people are initially vaccinated that they would need the next dose.
"From a public health standpoint, we don't know the answer to that, and we've got to be humble enough and modest enough to say we just don't know when it will be," Fauci said. "But we need to be prepared that in case a year from now or 18 months from now we need to do [it]. We need to be prepared to give it with some degree of knowing what it's going to do."
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Dr. Amesh Adalja, an infectious disease physician with the Johns Hopkins Center for Health Security, said that to him, "the threshold for needing a booster shot would be if you saw fully vaccinated individuals getting breakthrough infections that are landing them in the hospital to a high degree."
Another indicator for a booster might be if those reinfected individuals were carrying enough virus in their bodies to be contagious to others. So far, Adalja said, there is just not enough data to suggest that's the case.
"We're not trying to eradicate Covid-19," Adalja said. "What we're trying to do is remove its ability to cause serious disease, hospitalization and death."
The United States has seen a steady decline in cases nationwide recently, a trend that infectious disease experts attribute to the success of the vaccines from Pfizer, Moderna and Johnson & Johnson.
As of Thursday, the Centers for Disease Control and Prevention reported that nearly 48 percent of the total U.S. population has had at least one vaccination dose. Two shots are necessary for full protection from both the Pfizer and the Moderna vaccines, while Johnson & Johnson's requires just one shot.
Clinical trials found that the vaccines used in the U.S. were safe and highly effective. Real-world use has mirrored that success, leading the CDC to suggest last week that people who have been fully vaccinated can safely forgo masks.