The contagious delta variant has complicated the country's COVID-19 recovery, and health care experts are again suggesting Americans cover their faces.
They're now advising all people, both unvaccinated and vaccinated, to wear marks in indoor and crowded settings. While the virus may have mutated, medical experts told ABC News people can wear the same masks they've used previously.
"The delta variant has raised the stakes," Maureen Miller, an adjunct associate professor of epidemiology at Columbia University's Mailman School of Public Health, told ABC News. "The most important thing about the masks is that you wear them properly."
Miller, a former epidemiologist for the New York City Health Department, said the N95 is the most secure mask to block out the virus and the variants, but due to higher prices and strained supplies, most people should consider other options, such as the cloth masks and surgical masks found in most stores.
The key thing is making sure the mask completely covers one's mouth and nose.
"If it's not covering your nose, or if it's on your chin, it's not going to protect you," Miller added.
Dr. Nicole Iovine, chief hospital epidemiologist with UF Health in Gainesville, Florida, also told ABC News that regular face coverings sold in stores should protect people from the delta variant. Iovine also said double-masking is a good strategy, especially if you're unvaccinated.
"We should think about it as layers of protection," she said. "If you're unvaccinated, the only layer you can have is wearing a mask and staying isolated. If you're vaccinated, you have strong protection, but with a mask on you're very, very protected."
Dr. John Brownstein, an epidemiologist at Boston Children's Hospital and an ABC News contributor, said the most important rule about masking during the delta surge is being aware of one's surroundings. Extra care must be taken in situations in which it's easier for air droplets to spread.
"If you're in a crowded, poorly ventilated room, it's a bigger risk than being out in the woods," he said.
Miller recommended that vaccinated Americans should be masked up in any location where they're indoors and may be in contact with someone 12 years old or younger, because they're not yet vaccine eligible.
"The delta variant threw us a nasty curveball and set us back a step," Miller said. "All of the things that worked before -- social distancing, mask-wearing -- are all the things that will get us through this next round."
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