SAN FRANCISCO (CBS SF) — The Biden administration targeted the week of September 20th to have booster shots ready to go for Americans, Dr. Anthony Fauci said Sunday Pfizer may be the only one to meet that deadline.

Meanwhile, the Centers for Disease Control and Prevention is recommending that unvaccinated Americans not travel this Labor Day holiday weekend.

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The highly contagious Delta variant continues to fuel the surge, while only just over half of Americans are fully vaccinated.

In California, that number is higher at 66 percent, according to the CDC.

“Looks like Pfizer has their data in… We hope that Moderna would also be able to do it, so we could do it simultaneously, but if not, we’ll do it sequentially,” said Dr. Fauci. “The bottom line is very likely at least part of the plan will be implemented but ultimately the entire plan will be.”

The booster shots are subject to approval from the FDA and CDC.

UCSF infectious disease specialist Dr. Peter Chin-Hong says cases in the Bay Area are starting to flatten, though Labor Day weekend behaviors could change that.

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“Rather than quibble about third, or fourth, or fifth, sixth, or seventh dose, I’m really still worried about the vast swaths of people who are unvaccinated in this country even. We have the shots, I hope people go out and get them,” said Dr. Chin-Hong.

A new study out of Israel found that a third dose of Pfizer significantly improved protection from infection and serious illness among those 60 and older.

“There is precedent from other vaccines for a three-shot series,” said Dr. Chin-Hong. “We do know that lengthening the time between say a second shot and a third shot gives you a durable response, so it makes sense biologically to me, it’d be nice to see the data to support that.”

According to a CDC report released last week, COVID hospitalization rates for teenagers and children rose nearly five times from the end of June to mid-August.

“You’ll get more children infected and in fact when they get infected just on a pure basis of the relative number of people that will actually get into the hospital, you’re going to wind up seeing more children in the hospital,” said Dr. Fauci.

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He added that studies are underway about whether Americans can mix vaccines, and data should be available within a couple of weeks. Right now, he is suggesting that you stick with the brand that you received.