Representatives of Pfizer met privately with senior U.S. scientists and regulators on Monday to press their case for swift authorization of coronavirus booster vaccines, amid growing public confusion about whether they will be needed and pushback from federal health officials who say the extra doses are not necessary now.

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.

The twin developments underscored the intensifying debate about whether booster shots are needed in the United States, at what point and for whom. Many American experts, including Dr. Anthony S. Fauci, President Biden’s chief medical adviser for the pandemic, have said there is insufficient evidence yet that boosters are necessary. Some, though, say Israel’s move may foreshadow a government decision to at least recommend them for the vulnerable.