The Biden administration announced plans Wednesday to offer boosters to all U.S. adults as soon as next month, saying that recent data, including some made available only in the past few days, played a role in that decision.

“If you wait for something bad to happen before you respond to it, you find yourselves considerably behind,” Dr. Anthony Fauci said during a White House briefing. “You want to stay ahead of the virus.”

White House officials emphasized that the rollout of boosters was pending review of evidence by officials at the Food and Drug Administration as well as the advisory committee to the Centers for Disease Control and Prevention.

The rollout would begin the week of Sept. 20. U.S. residents 18 and older who received the Moderna or Pfizer-BioNTech vaccines would be eligible for a third shot eight months after their second dose. The timing would mean that health care workers, long-term care residents and older residents would be first in line for boosters.

“If you are fully vaccinated, you still have a high degree of protection from the worst outcomes — we are not recommending you go out and get a booster today,” U.S. Surgeon General Vivek Murthy said. Johnson & Johnson vaccines were not distributed until March and a plan for those booster shots will come later, officials said.

Political and corporate pressure to offer a booster to U.S. citizens has been mounting over the summer months, as the highly contagious delta variant has spread nationally and filled hospital beds. On Wednesday, Biden officials offered slides filled with charts of recent data, talked about antibody response, and noted that research showing waning vaccine strength in Israel played a key role in their decision as did a study from Mayo Clinic that is not yet peer-reviewed.

“Stick to the advice from the CDC and the FDA, because they are doing their very best to ensure maximum protection and safety,” said Dr. Cody Meissner, a specialist in pediatric infectious diseases who sits on the FDA’s vaccine advisory panel. “People have to be very careful about statements that come from Big Pharma. They have a very different goal.”

Dr. Sadiya Khan, an epidemiologist and cardiologist at Northwestern University’s Feinberg School of Medicine, said that taking any medication has risks and that adding an additional dose of vaccine might cause unnecessary side effects. “What we need is data,” she said.