In Pennsylvania, 65% of adults are fully vaccinated against COVID-19.

(CNN/KDKA) — Dr. Anthony Fauci urged the public to get vaccinated and said if the “overwhelming majority” of the population does so the U.S. could have the pandemic “under control” by spring of 2022.

“We hope we’ll be there … but there’s no guarantee because it’s up to us,” Fauci, director of the National Institute of Allergy and Infectious Diseases and the President’s chief medical adviser, told CNN’s Anderson Cooper Monday.

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It isn’t yet clear to health experts what proportion of the population needs to be vaccinated to reach a level of protection that could sustain a return to normalcy, like safely going to restaurants and theaters, Fauci said. So the best way forward is to vaccinate as many people as possible, he said.

About 51.5% of the population is fully vaccinated, according to data from the US Centers for Disease Control and Prevention. On Monday, the US Food and Drug Administration granted full approval to the Pfizer/BioNTech Covid-19 vaccine for people 16 and older, a move that Fauci said could convince a significant portion of hesitant Americans to get vaccinated.

Still, Fauci’s spring 2022 timeline is daunting politically for President Joe Biden, who already declared partial victory over the virus on July 4. In addition, CNN chief medical correspondent Dr. Sanjay Gupta questioned the definition of what it means to “control” a virus that looks to be here for the long haul.

“This is one of those situations where I think defining what it means to be in control of the pandemic is really important,” Gupta said Tuesday.

“If we have more people vaccinated, it’s likely we will decouple hospitalizations from cases, and maybe that will be a definition of control. (If) people aren’t getting that sick anymore, ending up in the hospital, the virus starts to slowly not have places to circulate, that will be a definition of control. I think we’re going to see waves of this for some time,” he added.

However defined, Covid-19 is certainly not under control now. Hospitals in many states with lower vaccination rates are overwhelmed by a surge in patients, students are returning to the classroom only to have to isolate due to exposure and cases among children are on the rise.

Pennsylvania’s Covid-19 vaccination totals topped 12 million on Monday, with 65% of adults fully vaccinated. Gov. Tom Wolf said he hopes the full FDA approval pushes those on the fence to talk to their health care providers.

But some experts are skeptical that vaccination rates will go up just because of the approval.

“I do think there will be a modest increase, but, look, we have a long way to go to fill this gap,” said Dr. Peter Hotez, vaccinologist and dean of the National School of Tropical Medicine at Baylor College of Medicine. “I think having the full approval will certainly convince some, but it’s just one of a dozen fake talking points put out there by the disinformation campaign. And, I think a number of people are just going to revert to one of the other ones.”

Several false claims about Covid-19 vaccines have posed a challenge to vaccinating greater numbers of Americans, Dr. Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, said Monday. Some of those include false claims about infertility, microchips and fatalities.

“Let me be clear: These claims are simply not true. Getting a Covid-19 vaccine can save your life,” Marks said.

The thing that may really motivate people to get those life-saving vaccines, Hotez said, is if the authorization paves the way for employers, businesses and schools to mandate vaccinations.

Fighting the Delta variant

One factor that has raised concerns over Covid-19 spread is the more transmissible Delta variant.

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Pfizer is making a vaccine specifically targeting the Delta variant, but Pfizer CEO Albert Bourla said Monday he doesn’t think it will be needed because the current vaccine is so effective.

“We are making right now a specialized vaccine for Delta,” Bourla told NBC. “I’m almost certain that we will not need it.”

Officials have begun preparing for the administration of boosters to protect against the variant in the fall and winter. But health experts say the measure is a precaution — and not a sign that the vaccines already in use are ineffective.

“There are various real-world evidence that are emerging here that suggest that the vaccine is still effective against the Delta variant,” Marks said. “Data coming out of Israel seems to suggest that with time, immunity from the vaccine does tend to wane, and so that’s something we’ll be following closely.”

Children still on hold

As health experts celebrate the first full approval of a Covid-19 vaccine, many are still left with questions about how children will be protected.

The approval only extends to adolescents 16 and older, meaning those ages 12 to 15 are still being vaccinated under emergency use authorizations. And many parents have awaited vaccine protection for children even younger.

The FDA emphasized Monday that the approval does not mean the vaccine can be used “off-label” in children younger than 12, saying “it would not be appropriate.”

Off-label refers to an approved product being used in a way or in a patient that it wasn’t necessarily approved for.

Vaccines for that age group are still in progress, and enough data for them could be available by mid-fall for Pfizer and a bit later for Moderna, Fauci said.

The FDA will then look at the data and make a risk benefit analysis, Fauci said.

“That could be a couple of extra months, so we don’t know whether or not we’re going to get the regulatory decision by the late fall, early winter or it might even go into the following year,” Fauci said.

Fauci said the decision to authorize the vaccine for this age group is “fundamentally based on safety.”

“I don’t think there’s going to be any question that this is going to be effective in the children at that younger age. I have no doubt about that,” Fauci said. “It’s going to be a safety issue.”

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