The earliest people to be vaccinated for COVID-19 may need booster shots as early as September, the CEOs of Pfizer and Moderna said.

In an interview with Axios on Wednesday, Pfizer CEO Albert Bourla stressed that the company is still awaiting data from clinical trials, but he believes people will need an additional dose between eight and 12 months after receiving their second shot. 

“This could become sooner than later, I believe, from September, October,” Bourla said. “But this is something again that the data need to confirm.”

Bourla added that the Food and Drug Administration and Centers for Disease Control and Prevention would have to sign off on the boosters. 

The two-shot vaccines developed by Pfizer and Moderna received emergency use authorization from the Food and Drug Administration in December.

Moderna CEO Stéphane Bancel had a similar prediction to Bourla’s, telling Axios in an email that he would recommend booster shots be administered starting in September to those who received their second doses in January. Bancel noted that the first wave of Americans to be vaccinated included high-risk populations such as the elderly and health care workers.

"I think as a country we should rather be two months too early, than two months too late with outbreaks in several places," Bancel said.

Johnson & Johnson, which developed the only other COVID-19 vaccine currently authorized in the U.S., did not immediately respond to a question from Spectrum News on Thursday about whether it foresees a booster shot being needed.

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases and President Joe Biden’s chief medical adviser, said Wednesday that he believes booster shots will be necessary within a year of initial vaccination. 

“We know that the vaccine durability of the efficacy lasts at least six months and likely considerably more,” he told Axios. “But I think we will almost certainly require a booster sometime within a year or so after getting the primary because the durability of protection against coronaviruses is generally not lifelong.”

Booster shots could also potentially help combat variants.

Last week, David Kessler, the White House COVID-19 response team’s chief science officer, said boosters would be provided for free to the American public if needed to keep the pandemic at bay.

"We are planning — and I underscore the word ‘planning’ — to have booster doses available if necessary for the American people,” Kessler told the Senate Health Committee.