Mask guidance continues to change. Here’s what you need to know, depending on who you are, to protect yourself—and, most importantly, others.
When the CDC announced in mid-May that fully vaccinated people no longer needed to wear masks in most indoor settings, it felt like a milestone to many Americans, indicating that we might be one step closer to the end of the pandemic. It’s understandable, then, that the agency’s decision several weeks ago to bring back indoor mask recommendations even for vaccinated people led to anger, frustration, or confusion for many.
“It is a little bit confusing that the public is told at one point that the vaccine is effective enough that they can pretty much ditch their mask anywhere, and now, this is clearly a different recommendation because of the very high transmissibility of the Delta variant,” Dan Diekema, an infectious disease epidemiologist at the University of Iowa College of Medicine, says. “I think the CDC did the right thing, but it definitely puts members of the public in kind of a difficult situation in terms of making day-to-day decisions.”
But now that the circumstances have shifted, so should our behavior to deal with them.
“The vaccines are highly effective, but we know they’re not perfect, so it’s important to use complementary measures like masking for those areas with higher levels of Covid in the community,” Saskia Popescu, an epidemiologist at the University of Arizona, says.
But that doesn’t mean everyone has to mask up everywhere outside their house, vaccinated or not. Let’s break down when to wear a mask and why, and when you can set it aside.
Why Vaccinated People Still Need to Mask
First, let’s briefly review why the CDC changed their guidance in May, and then again more recently. The clinical trials for the Covid-19 vaccines tested how well the vaccines prevented disease, and they did that remarkably well. Then data in spring revealed the vaccines also appeared to prevent most infections, as in the ability of the virus to begin replicating after getting into the body. That’s unusual—most vaccines don’t prime the body so well that it can dispatch a pathogen before it even begins hijacking cells—but it appeared to be true for the mRNA vaccines. Blocking infection also blocks transmission: If the virus never starts replicating, you never shed it, so you’re not infectious to anyone. Hence the CDC’s advice in May that vaccinated folks can ditch their masks.
Along comes Delta. Though not actually “as contagious as chickenpox,” despite the CDC’s leaked internal document, Delta is about twice as contagious as the original coronavirus strain that swept the nation in 2020. According to a recent study, it has a basic reproduction number (R0) of 5-9, which means a person infected with the Delta variant of SARS-CoV-2 will infect about 5 to 9 other people on average, instead of the 2 to 3 of the previous strains. (Since R0 is an average, some people will infect no one, and others may infect twice as many people.)
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Based on the most recent data, it seems Delta is so contagious because it replicates very quickly, producing about 1,000 times more virus particles than the original strain did. That’s partly why people infected with Delta become contagious sooner than with past variants, and it’s possibly why Delta seems to cause more breakthrough infections—but a mask reduces that risk further.
“People with Delta are shedding more virus, and if you’re around them for a long period of time, you’re going to be exposed to the minimum infectious dose in a shorter period of time than you would have otherwise,” Angela Rasmussen, a virologist at the Vaccine and Infectious Disease Organization-International Vaccine Centre in Saskatchewan, Canada, says. “Wear a mask, reduce the numbers. It’s that simple.”