Timeline: CDC mask guidelines during the COVID pandemic

The story of mask requirements in the United States has had many twists and turns since the early days of the pandemic, when the U.S. surgeon general urged Americans to "STOP BUYING MASKS!"

Since then, government and public health leaders have urged us to wear face masks even when walking around our neighborhoods alone, and told us to keep wearing them even after receiving the protection of highly effective vaccines.

It wasn't until May that the Centers for Disease Control and Prevention told fully vaccinated Americans that they could be exempt from nearly all mask requirements. The state of California followed suit with rules that went into effect when the economy reopened on June 15.

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The CDC recommends that even vaccinated people wear masks indoors in parts of the U.S. where the coronavirus is surging.

Now, as the highly transmissible Delta variant causes coronavirus cases to spike across the nation, indoor mask mandates are back in L.A. County regardless of vaccination status, and the CDC has updated its guidance as well. On Tuesday, the agency advised that vaccinated people return to wearing masks indoors in parts of the U.S. where the virus is surging.

Here's a brief timeline of official rules and guidance regarding face masks.

U.S. Surgeon General Dr. Jerome Adams tweets that wearing a face mask will not prevent the public from contracting the novel coronavirus.

"Seriously people — STOP BUYING MASKS!" he wrote in a tweet that was later deleted. "They are NOT effective in preventing general public from catching #Coronavirus, but if healthcare providers can't get them to care for sick patients, it puts them and our communities at risk!"

Even as the coronavirus spreads across the United States — shutting down businesses, sporting events and schools — the CDC's advice around masking remains unequivocal: Healthy people who do not work in the healthcare sector and are not taking care of an infected person at home do not need to wear masks.

"Facemasks may be in short supply and they should be saved for caregivers," the government agency says.

After insisting for weeks that healthy people did not need to wear masks in most circumstances, federal health officials change their guidance in response to a growing body of evidence that people who do not appear to be sick are playing an outsize role in the COVID-19 pandemic.

"The transmission from individuals without symptoms is playing a more significant role in the spread of the virus than previously understood," President Trump says when announcing the new advice at a White House briefing. "So you don't seem to have symptoms and it still gets transferred."

The new guidelines recommended masks for all people over age 2 who were in a public setting, traveling or around others in the same household who might be infected.

The CDC publishes a study that finds masking to be a "likely contributing factor" for preventing two coronavirus-positive employees of a Missouri hair salon from infecting any of the 139 clients they served.

"I think we’re being very clear now," says Dr. Robert Redfield, director of the CDC. "Now's the time to wear a mask."

He added that the U.S. could get the COVID-19 pandemic under control in one or two months if every American wore a mask.

The CDC releases color-coded guidelines to help local communities think through when it is safe to open schools for in-person learning. Even among schools with the lowest risk of community transmission, masking remains an important part of the CDC's guidelines for opening schools safely.

The agency recommends students and teachers wear masks whenever feasible. It also advises that schools spread out students’ desks, stagger their schedules, eat meals in classrooms instead of the cafeteria and add physical barriers between bathroom sinks.

Scientists report that if 95% Americans wore face masks when they left their homes, they could save well over 100,000 lives — and perhaps more than half a million — through the end of February.

"The potential life-saving benefit of increasing mask use in the coming fall and winter cannot be overstated," wrote the team from the Institute for Health Metrics and Evaluation at the University of Washington.

On his first day as president, Joe Biden signs an executive order requiring masking and physical distancing in federal buildings, on federal lands, and by government contractors.

Biden signs 10 executive orders aimed at jump-starting his national COVID-19 strategy — including one that requires Americans to mask up for travel. The new rule applies to airports and planes, ships, intercity buses, trains and public transportation.

Building on Biden's executive order, the CDC issues an 11-page order requiring travelers on airplanes and those using public transportation such as buses and subways to wear face masks to curb the spread of COVID-19.

The order makes refusal to wear a mask a violation of federal law, enforceable by the Transportation Security Administration and other federal, state and local authorities.

The CDC releases new guidelines allowing Americans who have been fully vaccinated against COVID-19 to shed their masks while visiting with others in small indoor gatherings. Social distancing isn't needed either, the guidelines say.

"You can visit your grandparents if you have been vaccinated and they have been too," says Dr. Rochelle Walensky, the CDC's new director.

The agency still recommends all people — vaccinated or not — remain masked when out in public.

As coronavirus cases drop, the CDC releases new guidance saying that people do not need to wear masks outdoors when they walk, bike or run alone or with members of their household. This applies regardless of vaccination status.

In addition, the agency says fully vaccinated Americans don't need to wear masks outdoors at all unless they are in a big crowd of strangers, such as a sporting event or an outdoor concert.

The CDC recommends unvaccinated people continue to wear masks at outdoor gatherings that include other unvaccinated people.

As the United States continues to see dramatic improvements in coronavirus case numbers, federal officials announce a sweeping relaxation of face mask guidelines that allow fully vaccinated people can stop wearing masks in most places — either outdoors or inside.

"Anyone who is fully vaccinated can participate in indoor and outdoor activities, large or small, without wearing a mask or physical distancing," Walensky says. "If you are fully vaccinated, you can start doing the things you have stopped doing because of the pandemic."

Under the federal guidance, unvaccinated or partly vaccinated people are still asked to wear masks in almost all indoor settings and most outdoor venues when interacting with people from outside their household who may not be vaccinated.

The agency also says that people should defer to local guidelines. California, for example, waits until June 15 to lift masking requirements for vaccinated people in most public places.

With the highly transmissible Delta variant fueling yet another increase in coronavirus cases and COVID-19 hospitalizations and deaths, the CDC recommends that fully vaccinated people return to wearing masks indoors in parts of the U.S. where the coronavirus is surging.

Federal scientists cite new information about the ability of the Delta variant to spread among vaccinated people as a reason for the change. As of July 19, the CDC had received reports of 5,914 fully vaccinated people who developed "breakthrough cases" of COVID-19 and were hospitalized or died. They represent less than 0.004% of the more than 161 million people who have been vaccinated in the U.S.

The new guidance follows decisions in Los Angeles County and St. Louis to revert to indoor mask mandates.

The CDC also recommends that masks be worn indoors by all teachers, staff, students and visitors to schools, regardless of their vaccination status. This aligns with California's previously announced plan to require face masks of everyone on K-12 campuses.