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There have been some bright spots recently in the fight against Covid-19: Infection rates are dropping in most states, more and more Americans are becoming eligible for vaccination, and the Food and Drug Administration now says the Johnson & Johnson vaccine meets the requirements for emergency use authorization. Meanwhile, new research finds that the Pfizer and Moderna vaccines are not only effective at preventing illness, hospitalization, and death, but they’re probably quite effective at preventing transmission, too.
But the optimism is tempered somewhat by the spread of more contagious Covid-19 variants, like B.1.1.7 and 501Y.V2, initially discovered in the UK and South Africa, respectively. Experts say the B.1.1.7 variant could be dominant in the US by March.
That means we need to be more careful about protecting ourselves. To do that, public health officials are recommending that people make a greater effort to avoid indoor spaces like grocery stores and double-mask when going indoors in a public setting.
Which has some people wondering: Should we be more careful outdoors, too? Do we now need to stay more than 6 feet away from our friends around that fire pit? What about those joggers who seem to be perpetually running toward us, unmasked?
Epidemiologists say they’ve been seeing these questions pop up a lot, and while it’s totally understandable to wonder about outdoor risks, it’s also somewhat misguided.
“There seems to be a bit of a fuss about needing to be more wary of transmission outdoors, but I don’t know where that has come from,” Richard Lessells, an infectious disease specialist at University of KwaZulu-Natal in South Africa, told Vox. “Based on the evidence, we still think risk of transmission outdoors is very substantially less than indoors, and there’s no reason to believe the new variants change that equation substantially.”
Muge Cevik, a virologist and physician at the University of St. Andrews in Scotland, told me there are “many things to worry about — outdoor brief contact is not one of them.”
Therefore, outdoor risk is negligible unless it involves close interaction or you are in a crowded or semi-outdoor environment. For example, walking on the street with no f2f contact, or passing by a jogger, the risk is very low as the duration of interaction is brief. (7/n)
— Muge Cevik (@mugecevik) January 11, 2021
That’s because, as I’ve explained before, a perfect sequence of events has to happen for a virus to move from an infected passerby outdoors to you.
The passerby has to spray out enough particles to be able to kick-start an infection. The virus inside the particles has to survive as sunlight, wind, and other forces work to decay and disperse them. The particles have to land in your upper throat or respiratory tract — or on your hands, which you then use to touch your eyes, nose, or mouth — and they have to get past all the barriers to infection in the respiratory system, like nose hairs and mucus. Then they have to dock up with your cells’ ACE-2 receptors and use them to enter the cells.
Even given what we’ve learned over the past months about airborne transmission, this is a pretty arduous sequence for viral particles to execute properly.
“The volume of distribution of gases within an outside space, particularly with a wind factor, makes this risk very low,” Cevik said. “A variant may be more transmissible, but physics has not changed.”
Low risk is not zero risk, of course. Close or prolonged contact with others (especially unmasked) or settings where there are lots of people should be avoided even if outdoors. But the main risk we have to worry about is still indoors.
What makes the new variants more contagious?
We know that the new variants spread between people more easily — but how do they do so? We’ve got some preliminary clues, but we still don’t have conclusive answers.
Angela Rasmussen, a Georgetown University virologist who agrees there’s minimal risk outdoors, nonetheless warns that there’s still much we don’t know about the new variants. “It’s really hard to say if we need to be more careful with outdoor interactions with the new variants because we don’t know the mechanism by which they are more transmissible,” she told me. “Is it that people shed more virus? The virus is more efficient at causing infections? Is the virus more stable in the environment?”
Since January, Cevik has suspected that the virus has gotten better at binding to the receptors in human cells. Both the B.1.1.7 and 501Y.V2 variants feature a lot of mutations in the virus’s spike protein, the piece that fits into the receptors. And if a variant is better at attaching to receptors, then once people are exposed to it, they may be more likely to get infected — even if the sick person they’ve encountered isn’t shedding more virus.
New lab research has demonstrated that increased receptor binding is in fact happening with these variants. There may be other factors at play, too. Better receptor binding could influence the infectious dose (the amount of virus needed to launch an infection).
It could also lead to a longer infection. Some new data gathered from NBA players suggests that with B.1.1.7, people stay infectious for longer, which could be upping the transmissibility: People may think they can safely stop quarantining after 14 days, but then they pass the infection on to others. (This is already sparking debate about whether we should extend quarantine guidelines, but it’s worth noting that the NBA evidence is from only seven players, a very small data set.)
Further studies on more potential processes underlying transmission — like how fast the variants replicate in the body and how long the variants survive in the environment — are pending. Cevik says we’ll be able to understand these dynamics more in a few weeks.
So, for now, what should we do outside?
The variants make everywhere a bit riskier than before. According to Boston University epidemiologist Eleanor Murray, “It’s still unlikely that you would get infected passing an unmasked jogger, but the risk of that is now a bit more like passing two unmasked joggers.”
But the ways the virus spreads are still the same. So, Rasmussen said, “I don’t think that staying 6 versus 10 feet [apart] matters much outdoors. What might be more useful to think about is the nature of outdoor contacts. Are there lots of people? Are they wearing masks? Is it fully outdoors or in some kind of partial enclosure?”
The experts I spoke to recommended sticking to smaller group sizes and wearing a mask outdoors (at least one mask; two if you want to be extra careful). After all, if the variants lead to higher community prevalence in your area, you’ll be more likely to come across someone who is infectious.
But let’s not lose sight of the fact that the greatest risk is still indoor interactions.
“The main risk with the variant, I would say, is indoors now, because earlier evidence suggests that it clusters more in households compared to older variants, and more people are spending time indoors now,” Cevik said. “We are seeing significant outbreaks in nursing homes and hospitals due to the new variant.”
So it makes sense to cut ourselves some slack outdoors, and avoid shaming others for their outdoor activities. “There’s a delicate balance between preventing infections and increasing lockdown fatigue,” she wrote. “People do not have unlimited energy, so we should ask them to be vigilant where it matters most, which is indoors, while giving them a break outdoors.”
