(CNN) Dr. Anthony Fauci says there are five or six things to keep the spread of the coronavirus in check. And he says he will continue to repeat those public health principles "until I'm exhausted" because "those things work."
"Universal wearing of a mask, physical distancing, avoid crowds, outdoor better than indoor, washing your hands and hand hygiene -- and if you're in a situation where it applies to you, stay away from bars," he said during a webinar with the Brown School of Public Health.
Dr. Fauci says wearing a mask and opening up the country go hand in hand.
He says somewhere down the line, it became "there's public health principles, and then there's open up the country." But that shouldn't be the case.
"We really need to get that point across, that one is not the enemy of the other. One is a gateway to get to the other," Dr. Fauci said.
He added that he hopes somehow the country will become unified and battle Covid-19 together.
"I don't think we need to go into the fall and the winter thinking we're going to have a catastrophe. We could go into the fall and the winter, coming out of it looking good, if we do certain things," Dr. Fauci added.
At a news briefing in Baltimore, US Surgeon General Dr. Jerome Adams echoed Dr. Fauci's point of view.
"We don't need to wait for a vaccine. We don't need to wait for a miracle therapeutic," he said.
Dr. Adams says New York City and the state of New York have a positivity rate of less than 1% by following three things.
"They've done it with three things -- what I call my Three W's. Number one, wash your hands. Number two, watch your distance -- meaning stay at least six feet from others and avoid crowded places. And number three, wear a face mask," he added.
But he warned it takes time for the results to be seen. "We just need to stay the course and continue to normalize that positive behavior," Adams added.
Dr. Fauci and Dr Adams' words come as the death toll tops 10,000 in California, according to data from the California Department of Public Health (CDPH). The state also has more than 541,000 positive cases.
However, the CDPH is warning that there has been an underreporting of cases due to issues with the state's electronic laboratory reporting system. The positivity rate over a 14-day period is now 6.1%, according to the CDPH.
While California has the highest number of cases in the nation, the death toll is still well below that of New York and New Jersey.
US coronavirus deaths could hit 300,000 by December 1, but 70,000 lives could be saved if more Americans simply wore masks, a new model predicts.
"It's a profoundly sad number" of projected death, Dr. William Schaffner of Vanderbilt University told CNN on Friday morning. "And we can think that 70,000 of those people could be saved if we would all just wear a mask every day every time we leave our front doors.
"This virus Is not just going to disappear or vanish. The virus is with us, and we're going to have to combat it, and the simple thing that we can all do is wear a mask. Please, everyone, wear your mask every day," Dr. Schaffner said.
Added CNN chief medical correspondent Dr. Sanjay Gupta on Friday: "That number of lives saved could be even higher if we did this," noting that masks could cut transmission by more than the model's basis of 40%.
As the number of US cases races toward 5 million, the Covid-19 pandemic is moving into younger populations, health experts said Thursday, with cases skyrocketing among children, teens and young adults.
Early in the outbreak, health experts stressed that older adults were most at risk, but new data from the World Health Organization shows that most cases -- by far -- are among people 25 to 64 years old. The proportion of cases in teens and young adults has gone up six-fold, and in very young children and babies the proportion has increased seven-fold, WHO said.
The increase might be explained by broader testing, greater detection of milder cases and shifting demographics of hot spots, but "a rise in risky behavior after easing of public health and social measures" is also to blame, WHO said.
But testing is actually down in 29 states, with "no perfect test available to us" and too many false negatives, said Anne Rimoin, a professor at UCLA's Department of Epidemiology on Friday. "Testing needs to be expanding, not contracting. And we really need to keep an eye on positivity rates."
Many Americans live in "diagnostic desserts" and must wait weeks for results, said Susan Butler-Wu, associate professor of clinical pathology at the University of Southern California.
"The labs are overworked," she said. "The system is broken right now."
In Georgia, a 7-year-old child with no underlying conditions became the youngest person in the state to die of the virus.
In New Mexico, where a fifth of cases are among people 20 to 29, the state's Human Services Secretary Dr. David Scrase urged people not to plan big gatherings for Labor Day.
"Just do that cookout with the people you live with," Scrase said Thursday. "Don't get the family together. There will be more time to do that."
But school sports should reopen, said Florida Gov. Ron Desantis, because the reward is worth the risk to kids.
His own children are not old enough for sports yet, he said.
"But if they were, I would want them playing, and if they bring something back to the house, as much as I wouldn't want that, I would rather take that risk than deprive them of the opportunity to do things like this," Desantis said.
In Georgia, everyone should continue wearing masks, washing hands and practicing social distancing to bring down infection rates, Lt. Gov. Geoff Duncan told CNN Friday. He was responding to questions about a photo showing a crowded hallway in a high school where students are not required to wear masks -- and most did not.
The state allows local districts to set their own rules about preventive measures, he said.
Across the country, more than 160,000 people have died of coronavirus so far, and that number could nearly double by December, the director of a leading model said Thursday.
But consistently wearing masks could save 70,000, the University of Washington's Institute for Health Metrics and Evaluation (IHME) director Dr. Christopher Murray said on CNN's Global Town Hall.
"It's rare that you see something so simple, so inexpensive, so easy for everybody to participate in can have such an extraordinary impact in the US and also all over the world," Murray said.
At least 39 states as well as Washington DC and Puerto Rico have mask requirements. Kentucky Gov. Andy Beshear on Thursday extended his mandate by 30 days, saying, "It's working."
The US Centers for Disease Control and Prevention updated its website, urging people not use masks with valves or vents. While the one-way valve keeps people cooler, it also means respiratory droplets that carry the virus can escape and infect others.
Vaccines are being developed quickly, but health experts caution they will only be released to the public once they are safe.
"When the vaccine becomes available after a 30,000-person-or-more placebo-controlled randomized trial, and it's shown to be safe and effective, I would get it any time within the time frame of the people who prioritize it according to ethical principles," Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told the Politico Pulse Check podcast.
He said he is "satisfied" with the first week enrollment in Moderna's Phase 3 clinical trial for a coronavirus vaccine, which saw 1,290 people randomly assigned to get either the vaccine or a dummy shot. Moderna plans to enroll 30,000 people in its trial.
Fauci expects "to get an answer" about whether the vaccine works in November or December, he told CNN.
President Donald Trump hopes to know much sooner. He said Thursday he is "optimistic" that a vaccine could be ready by Election Day on November 3.
But giving specific dates for when a vaccine could be available is "very dangerous," former Surgeon General Dr. Vivek Murthy told CNN Thursday.
"We can't sacrifice our standards because if we do, it not only hurts people, but it's going to damage people's faith in vaccine efforts," Murthy said.
Federal officials have often been at odds with local leaders and health experts, and five former directors of the CDC said it is time for national leadership against the pandemic.
"It's unbelievable that six months into the pandemic, it's not clear who's in charge, federally," Dr. Thomas Frieden said during a roundtable hosted by ABC News Live. "There's no plan. There's no common data that we're looking at to see what's happening with the virus and what's happening with our response."
The CDC being sidelined early on and contradictory messages from the Trump administration has led to partisanship, confusion and increased spread of the virus, Frieden said.
"These are lives we can all save if we all wear masks, and we need national direction to do that," Vanderbilt's Schaffner said Friday.
In the absence of national leadership, state officials have been taking measures against the virus into their own hands.
Louisiana Gov. John Bel Edwards extended bar closures Thursday and announced the state will stay in Phase Two of its reopening plan, while New York City Mayor Bill de Blasio extended the city's state of emergency, which was first signed in March, for another 30 days.