Speaking with CBS This Morning on Thursday, Fauci said that “we don’t feel at this particular point that, apart from the immune-compromised, we don’t feel we need to give boosters right now.”

However, Fauci noted, health officials are following the progression and mutation of the virus in real time, and the situation is changing fast. It is “likely” that everyone will, at some point, need a booster shot, Fauci said, but he did not offer any projected timeline for when that might be.

Pfizer, in July, said it would begin seeking FDA approval for a booster shot this month. The company said initial data from an early human study showed that a third dose of its existing coronavirus vaccine is safe and can raise neutralizing antibody levels five- to 10-fold compared with the original vaccine.

Research from the Mayo Clinic earlier this week raised questions about the effectiveness of Pfizer’s shot versus Moderna’s against breakthrough infections. Pfizer showed a 42% efficacy, while Moderna had 76%.

“There is a lot of fear and concern” about variants, said Pfizer research head Mikael Dolsten at the time. “We are confident that such a boost will be highly effective against the Delta variant.”

Whenever booster shots do get approved, whether for immunocompromised people or others, Fauci said it will be best not to mix brands. In other words, if your initial jabs were with Pfizer, you should stick with Pfizer for the booster, not Moderna.

“It is preferable you go with the same brand,” Fauci said. “You will be hearing instructions about that from the FDA [and] through the CDC.”

“There will be guidance when that time occurs,” Fauci said.

Immunocompromised persons are those with weakened immune systems. This includes people with HIV/AIDS, cancer and transplant patients who are taking certain immunosuppressive drugs, and those with diseases that affect the immune system, such as lupus, Type 1 diabetes, and rheumatoid arthritis.