Different recommendations on boosters for different vaccines, they said, could confuse the public. Fully approving a vaccine and then authorizing a booster for it soon after might also offer conflicting messages about its effectiveness.
Understand the State of Vaccine Mandates in the U.S.
While research is continuing, senior administration officials increasingly believe that at the least, vulnerable populations like those with compromised immune systems and older people will need them, according to people familiar with their thinking. But when to administer them, which vaccine to use and who should get shots are all still being discussed.
In a study posted online last week, Pfizer and BioNTech scientists reported that the effectiveness of Pfizer’s vaccine against symptomatic disease fell from about 96 percent to about 84 percent four to six months after the second shot, but continued to offer robust protection against hospitalization and severe disease.
Administration officials said Moderna and Johnson & Johnson needed to present data as well and Moderna had been asked to do so quickly. Officials have said other studies will also influence their decision-making, including data that the government is collecting on the rate of breakthrough infections among tens of thousands of people, including health care workers.
Pfizer is expected to submit an application for a booster shot to the F.D.A. this month. While the F.D.A. could authorize such shots, the Centers for Disease Control and Prevention would need to recommend them after a meeting of its outside committee of experts.
A decision to fully approve Pfizer’s vaccine will give doctors more latitude to prescribe additional shots at least for certain Americans, including those with weakened immune systems. The C.D.C. had been exploring possible special programs for that group, but administration officials said it became clear that by the time any such initiative got underway, the Pfizer vaccine would already be fully approved and doctors could prescribe a third shot.
Roughly 3 percent of Americans — or about 10 million people, by some estimates — have compromised immune systems as a result of cancer, organ transplants or other medical conditions, according to the C.D.C. While studies indicate that the vaccines work well for some of them, others do not produce the immune response that would protect them from the virus.