As the highly transmissible delta variant sweeps across every state in the country as the dominant strain of COVID-19, public health experts warn now is not the time to ditch masks or forgo testing.
If anything, the United States, particularly in areas where vaccination rates have stalled and coronavirus cases are rising, is at an urgent juncture in the pandemic, in which continued mask-wearing and testing are pivotal because of how quickly the variant has been spreading, the experts say.
"I think it's critical to be masking indoors no matter where you live," said Susan Hassig, an epidemiologist at the Tulane University School of Public Health and Tropical Medicine, on Wednesday as her home state of Louisiana was poised to exceed the peak of hospitalized COVID-19 patients since the pandemic began.
Every parish in the state is at the highest risk level, of red, and Gov. John Bel Edwards, a Democrat, announced Wednesday an indoor mask mandate through at least Sept. 1 for anyone ages 5 and older who enter places like schools, businesses and churches, no matter their vaccination status.
"I can't tell you how different it feels than ever before," Hassig said. "This virus is moving so fast. More and more counties on the local levels are turning orange and red every day. It's critical to mask and test on suspicion of exposure."
Other parts of the South, including Florida and Tennessee, are also struggling with COVID-19 surges as their vaccination rates remain below 50% of their populations.
The Centers for Disease Control and Prevention is recommending masks be worn indoors in places with substantial or high COVID-19 transmission or test positivity rates, which is currently about 80% of all U.S. counties.
Karl Minges, the interim dean of the school of health sciences at the University of New Haven, said it's time for the majority of Americans to get back to early pandemic basics, no matter their vaccination status: Wear a mask, especially indoors; socially distance; and hand-sanitize. He said to try to continue most activities outdoors, whether eating or attending a concert, and be aware of how crowded it may be and what the COVID-19 positivity rate is for the area.
"The goal is to not return to the precautions of 2020, and that is unlikely the more people who become vaccinated," Minges added.
On Tuesday, New York City became the first major city in the country to require proof of vaccination for indoor activities at restaurants, gyms and performance spaces, with full enforcement coming in September. While about 55% of the city's population is fully vaccinated, the rate of new vaccinations has leveled off in recent months, and about 72% of tested cases of the coronavirus have been attributed to the delta variant, city health data show.
While many Broadway shows are still eyeing returns in September, major events are being scrapped because of the delta variant's rise. The 2021 New York International Auto Show at the Jacob K. Javits Convention Center in midtown Manhattan, which can draw about 1 million people, was canceled Wednesday, just two weeks before it was scheduled to start.
Elsewhere, it's business as usual: Concerts are selling out at near-record levels, and major festivals like Lollapalooza, which was in Chicago over the weekend and attracted hundreds of thousands of attendees, are going on as planned.
Attending an outdoor concert in small social bubbles if you are vaccinated and unmasked is OK and should be up to a person's comfort level, said Dr. Emily Landon, executive medical director for infection prevention and control at the University of Chicago Medical Center.
But that social setting is not the same as attending a large-scale event like a music festival where people are smushed together. The problem, Landon said, is the delta variant is more contagious than earlier forms of COVID-19, and at outings where large groups of people are interacting within a 6-foot radius, the window of time needed to transmit the virus is smaller.
"Before you had to spend 15 minutes inside your 6-foot radius; now you only need to spend a couple of minutes in there" for exposure, she said.
However, sporting events like a baseball game are different, she said, because people are typically socially distanced, may be wearing masks and often face outward, and even if they're waiting in a line, they're not bunched up in crowds like at a music festival.
Experts say masks are especially important if you're going to be around people whose vaccination statuses are unclear and you can't keep your distance.
"You probably could have gotten away with not getting masked in a workplace if everyone was vaccinated pre-delta," Hassig said. "But delta is different."
Hassig also suggested that people consider enforcing masks again for weddings and parties, even if they're outdoors, if there are no vaccination requirements and people are socializing in close proximity.
"You may have medically vulnerable people coming, and it's only reasonable to think about what you need to do so that Granny doesn't catch coronavirus," she said.
COVID-19 testing also should be utilized if someone is feeling sick or may have been exposed, experts say. Some employers, like big tech companies and government agencies, will require COVID-19 vaccinations for employees if they want to return to the office following months of working from home, and in some cases, those who refuse will be subject to regular testing.
Landon said fully vaccinated people don't need to get tested regularly but should if they have symptoms of COVID-19 or were exposed to someone who tested positive.
The CDC suggests fully vaccinated people get tested three to five days after exposure, even if the vaccinated person has no symptoms because they could be asymptomatic. So-called breakthrough cases of COVID-19 in which vaccinated people can get infected remains extremely rare, health officials say, and is not a failure of vaccines.
The CDC's recently updated mask guidelines were devised "to ensure the vaccinated public would not unknowingly transmit virus to others, including their unvaccinated or immunocompromised loved ones," CDC Director Dr. Rochelle Walensky said last week.
Hassig also suggested testing if you're going to be amid a large gathering where you don't know vaccination statuses — similar to what people were doing last summer when COVID-19 vaccines were unavailable.
Ultimately, because standard COVID-19 tests cannot specify whether someone has the delta variant, experts say it's safe to assume that if you test positive, you have the strain.
"That genie is out of the bottle," Hassig said, "and unfortunately, it's a really nasty one."
This story first appeared on NBCNews.com.