"We are now doing studies that are ongoing as we're speaking, studies that are looking at what we call age de-escalation, children from 12 to 9 and then 9 to 6 and then 6 to 2 and then 6 months to 2 years," Fauci, the director of the National Institute of Allergy and Infectious Diseases, told CNN's John Berman.
"We hope that as we approach the end of this calendar year, we'll have enough information to vaccinate children of any age," he said. "So, I'm cautiously optimistic we might be there by the end of the year."
The Pfizer-BioNTech COVID-19 vaccine is available for children age 12 and up, but those younger are not currently eligible to get vaccinated. Children under 12 are far less likely to have severe cases of COVID-19, but they can still get infected and spread it to others.
Vaccinating school-aged children is a key part of a safe return to normalcy for the education system. The CDC has advised schools to prioritize universal mask use, but it has also said vaccinated people have such strong protection that they do not need to wear masks in most situations.
In comments to NBC Nightly News on Wednesday, Fauci said if some communities continue to see high levels of infections, children under 12 will likely still have to wear masks when school returns.
The CDC considers a county to have "high" transmission if there have been 100 or more cases of COVID-19 per 100,000 residents or a test positivity rate of 10% or higher in the past seven days.
Dr. Rochelle Walensky, director of the US Centers for Disease Control and Prevention, said on Good Morning America on Thursday that school guidance is being revisited as more and younger people get vaccinated -- and there may be a change in school mask guidance in time for fall.
"We've said through the school year of '20 to '21 that our school guidance was not going to change," Walensky said when asked why children still need to wear masks. "What we really are doing now is looking at the evidence in the context of so many people getting vaccinated, in the context of disease rates coming down in certain communities and really looking at the evidence now.
"As we're starting to get those people vaccinated, we will be revisiting this in our school guidance," she added.
When asked if there might be a change to mask guidance in time for school in the fall, Walensky said, "I think we will. We are looking at the evidence now and we will be coming out with that guidance, soon to come."
More vaccinations, fewer infections
So far, more than half of the population has gotten at least one dose of vaccine and 12 states have reached President Joe Biden's goal of having 70% of US adults getting at least one dose by July 4.
As vaccinations have gone up, cases of the virus have gone down. Ensemble forecasts published Wednesday by the US Centers for Disease Control and Prevention project that newly reported COVID-19 cases, hospitalizations and deaths will likely continue to decrease over the next four weeks.
Fauci said the trends are very encouraging.
"The one thing we want to make sure is that we don't declare victory prematurely and feel that, because things are going in the right direction, that we don't have to keep vaccinating people," he said. "We're on a really good track now to really crush this outbreak. And the more people we get vaccinated, the more assuredness that we're going to have that we're going to be able to do that."
Current vaccination rates have begun tapering off -- and are now less than a third of the peak pace of about 3.3 million per day in April. But the July 4 goal is still realistic, Fauci said.
CNN medical analyst Leana Wen warned that after Memorial Day weekend, the US is still two weeks away from seeing the results of its first stress test, given that almost half of the country remains unvaccinated.
Even if cases plateau or taper off from their current falling rate, Wen said she worries some communities will remain vulnerable.
"You have parts of the country with very low vaccination rates," she said. "I really worry about the unvaccinated people in those areas spreading coronavirus to one another."
Fauci also said he's worried about communities that are experiencing high levels of spread. He told NBC News that it is too early to lift mask mandates in those areas.
"If you pull back on masking, then you're going to wind up having a danger of peaking again," he said.
New York City offering vaccinations in schools
Now that vaccines are available for children as young as 12-years-old, New York City will begin offering in-school vaccinations for kids 12-17, Mayor Bill de Blasio announced Wednesday.
The program will start at four schools in the Bronx on Friday and will eventually expand to all five boroughs in the next few weeks. The city is partnering with UFT, a labor union that represents most teachers in the NYC public school system, to get as many kids vaccinated before the school year ends later this month, de Blasio said.
Currently, around 118,000 New York City kids aged 12 through 17 have been vaccinated, comprising about 23% of the city's kids in that age range, de Blasio said.
After more than a year learning remotely, many people are eager to make schools a safe place for their students to return.
Studies are underway in hopes of making a vaccine available to children as young as 6 months. These trials may still take months in order to ensure the doses are safe and efficacious.
More vaccinations are an uphill battle
Significant mitigation strategies may be needed in areas where there is large-scale, community transmission, the CDC said, including in communal settings, like schools and workplaces.
As well as masks and social distancing, widespread vaccinations are key to reducing transmission, experts have said.
But after a quick surge of eager participants, the remainder are those who have often received false information about their safety or who lack access.
As a result, the road to vaccinating the rest of the population may be an uphill battle from here on out, the US Surgeon General Dr. Vivek Murthy said Wednesday, but "we're not giving up."
"Because we had so much success early on, we are now getting to the part of the campaign which is tougher," Murthy said "We've got to look further, if you will -- convince more people, get to the right information, increase access even further."
The early success is helpful in keeping large swaths of the nation protected -- but reaching the levels that will stop community spread will take a change in strategy, Murthy said.
"This is a multi-pronged campaign recognizing that people have different reasons that they're not vaccinated right now, but we have to work on all three fronts: mobilization, education and improving access," said Murthy. "That's how we're going to get the nation vaccinated."
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