More data showing people without symptoms are fueling the spread of coronavirus have top officials rethinking whether the general public should be wearing masks.
New data out of Iceland shows 50% of those who tested positive said they were asymptomatic.
In the US, an estimated 25% of coronavirus carriers have no symptoms, said the director of the Centers for Disease Control and Prevention.
"Information that we have pretty much confirmed now is that a significant number of individuals that are infected actually remain asymptomatic. That may be as many as 25%," CDC Director Dr. Robert Redfield told NPR.
More than 186,000 people in the US have been infected with coronavirus, and at least 3,888 have died.
To prevent further spread, the top infectious disease expert in the US says health officials are reconsidering guidance on face masks.
Dr. Anthony Fauci said he would "lean towards" recommending that the general public wear face masks "if we do not have the problem of taking away masks from the health care workers who need them."
"We're not there yet, but I think we're close to coming to some determination," Fauci said.
If federal officials recommend widespread use of face masks, it would be a stark reversal from recommendations by the World Health Organization and the CDC, who have said face masks should only be worn by health care workers, those who are sick, and those who are taking care of someone sick.
"There is no specific evidence to suggest that the wearing of masks by the mass population has any potential benefit," Dr. Mike Ryan, executive director of the WHO health emergencies program, said Monday.
"In fact, there's some evidence to suggest the opposite in the misuse of wearing a mask properly or fitting it properly."
3 tips for wearing a mask correctly
But this week, new information about asymptomatic spread could change public guidelines, Adams said. He offered several tips on how wear masks correctly.
"If you're going to wear a face covering, please try not to touch your face. Please be very, very careful about making sure you don't touch your face," Adams told NBC's "Today" show Wednesday.
Adams has said people often touch their faces trying to adjust masks, thereby increasing the risk of infection.
"No. 2: If you're going to wear a face covering, please save the N95 masks for healthcare workers who need them," Adams said. N95 respirators must be properly fitted to ensure there's no open space, and people with no medical training might wear them incorrectly.
"No. 3: Wearing a face covering does not mean that you don't have to practice social distancing," he said.
"The most important thing you can do is stay at home right now. And we don't want people to feel like, 'OK I'm covering my face, so now it's OK for me to go out in public.'"
A major argument against the widespread use of masks is that health care workers don't have enough.
"We have a massive global shortage," Ryan said. "Right now, the people most at risk from this virus are front-line health workers who are exposed to the virus every second of every day. The thought of them not having masks is horrific."
So some people are making their own masks. JOANN Fabrics and Craft Stores released a video tutorial on how to make face masks.
The height of the coronavirus pandemic is yet to come
White House officials predict more than 100,000 people could die from coronavirus -- and that's if the public practices social distancing guidelines perfectly.
By mid-April, when the virus is projected to hit the country the hardest, as many as 2,000 Americans could die each day, a model cited by the White House shows.
Health officials saying measures working to curb the spread of the virus are the only hope for keeping the death toll in the thousands and not millions.
If Americans don't follow social distancing guidelines, worst-case modeling projects up to 2.2 million people could die, said Dr. Deborah Birx, the White House coronavirus response coordinator.
More than two dozen states have issued stay-at-home orders, and the federal government extended social distancing guidelines to last through April 30.
Birx said there's no easy way to fix the coronavirus pandemic. It's up to the public to help stop the spread.
"There is no magic bullet," she said. "There is no magic vaccine or therapy. It's just behaviors. Each of our behaviors translating into something that changes the course of this viral pandemic over the next 30 days."
Evidence shows social distancing helps
About 80% of the US population has been ordered to stay at home, according to a CNN count. That count includes state, city and county orders.
Health officials say social distancing efforts seem to be paying off, including in Washington state's King County -- the country's first coronavirus epicenter.
"We are looking at reductions in person-to-person contact that have progressively improved and have led us to a point where we are making a very positive impact," said Dr. Jeff Duchin, the public health officer for Seattle and King County.
In hard-hit New York, a CNN analysis shows the day-to-day average of case increases in the past week was 17% -- a major decrease from 58% for the previous seven-day period.
An a large-scale study found that early interventions, such as social distancing and severe restrictions on people's movement, have already saved tens of thousands of lives across Europe.
Scientists at imperial College London studied interventions in 11 European countries and concluded that they "have together had a substantial impact on transmission."
The researchers estimate as of March 31, "interventions across all 11 countries will have averted 59,000 deaths."