The first Americans to be vaccinated against the coronavirus could require a third "booster" shot as early as September, the CEOs of Pfizer and Moderna told Axios.

Driving the news: “The data that I see coming, they are supporting the notion that likely there will be a need for a booster somewhere between 8 and 12 months," Pfizer CEO Albert Bourla said yesterday during an Axios event.

That means some Americans could need a booster as soon as September or October, he added.

State of play: Only time will tell how long protection from the first two vaccine doses will last, but there's no evidence yet that it's fading. Even if protection does begin to fade — which is common among vaccines — it won't happen overnight.

• And as the virus continues to spread around the world, it’s possible that vaccine-resistant variants could eventually emerge. (The existing vaccines are highly effective against the variants currently circulating in the U.S.)

What they're saying: "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," NIAID director Anthony Fauci told Axios' Mike Allen at the same event.

• "I think as a country we should rather be two months too early, than two months too late with outbreaks in several places," Moderna CEO Stephane Bancel wrote in an email.
• "People at highest risks (elderly, healthcare workers) were vaccinated in December/January," he added. "So I would do [a] September start for those at highest risk."

The other side: Experts caution to consider the drug companies' predictions in context with their broader business goals.

• "It’s not proven that we need boosters yet. Whereas it’s appropriate to plan for boosters, you’ve got to look at whether there’s a corporate agenda behind this," said Cornell professor and virologist John Moore.
• “As of now, we don’t have any evidence that protective immunity has dropped to a troubling point, and certainly not for people immunized in December, January, February," he added. “It's hard to say where we will be in November because right now it’s May.”

The bottom line: Even if you received your first shot in December, you don't need to worry that you'll wake up tomorrow having lost all of your immunity.

• “Personally, if I was in that situation, I wouldn’t be worrying about it — not yet. But I would want to see that data later in the year," Moore said.
• The decline in protection would be gradual, and researchers around the world are gathering data on the subject through clinical trials and real-world evidence.