| Hey readers,
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 is meeting next week to review the Johnson & Johnson vaccine for emergency use authorization. But the optimism is tempered somewhat by the spread of the more contagious Covid-19 variants, 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 we make a greater effort to avoid indoor spaces like grocery stores and that we double-mask when we have to go indoors out in public.
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, a University of KwaZulu-Natal infectious disease specialist 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, told me there are "many things to worry about — outdoor brief contact is not one of them." That's because, as I've explained before, a perfect sequence of events has to happen for a virus to jump from an infected passerby outdoors to you. A big enough number of particles has to spray out of the passerby with a great enough force to reach you; the particles have to survive the sunlight and wind working to decay or disperse them; and they have to get past all the natural barriers to infection in your respiratory system (like nose hairs and mucus).
"A variant may be more transmissible, but physics has not changed," Cevik quipped.
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 still 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 more easily, but we don't know how they do so.
Angela Rassmussen, 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?"
Cevik suspects it's not that people are shedding more virus. "There were some discussions about increased viral load leading to more transmission, but according to the largest dataset, this does not seem to be the case. Patients with the variant had similar viral loads to those without the new variant," she noted, citing a preprint paper.
Instead, Cevik suspects the virus may have 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.
"Same viral load, just that the variant virus you are being exposed to is better at attaching to and infecting cells," Cevik explained. "So, once people are exposed to the virus, they may be more likely to get infected."
The lab studies seeking to confirm increased binding are still pending, but if that's confirmed as the underlying mechanism, it would at least suggest we don't need to worry that the virus has become more stable in outdoor environments.
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 in which the virus spreads are still the same. So, Rasmussen said, "I don't think that staying 6 versus 10 feet 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're like me and 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 get distracted from the greatest risk: indoor interactions.
—Sigal Samuel, @SigalSamuel |
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