The high-level online meeting, which lasted an hour and involved Pfizer’s chief scientific officer briefing virtually every top doctor in the federal government, came on the same day Israel started administering third doses of the Pfizer-BioNTech vaccine to heart transplant patients and others with compromised immune systems. Officials said after the meeting that more data — and possibly several more months — would be needed before regulators could determine whether booster shots were necessary... And any recommendations about booster shots are likely to be calibrated, even within age groups, officials said. For example, if booster shots are recommended, they might go first to nursing home residents who received their vaccines in late 2020 or early 2021, while elderly people who received their first shots in the spring might have a longer wait. And then there is the question of what kind of booster: a third dose of the original vaccine, or perhaps a shot tailored to the highly infectious Delta variant, which is surging in the United States. “It was an interesting meeting. They shared their data. There wasn’t anything resembling a decision,” Dr. Fauci said in a brief interview Monday evening, adding, “This is just one piece of a much bigger puzzle, and it’s one part of the data, so there isn’t a question of a convincing case one way or the other.”