Even I, for as COVID-cautious as I've been, have gotten pretty lax about outdoor events. A new study from China suggests we should be more careful. Three infected people attended a crowded night market, and they infected at least 131 other people. The market was crowded and there was little wind. Researchers found #COVID19 aerosols released by patients could suspend in ambient air up to 1 h 39 min and still be contagious. https://www.frontiersin.org/articles/10.3389/fpubh.2023.1153303/full
Important to note it was a *night* market, which means there was no benefit from UV radiation. A good reminder that outdoors isn’t magically safe, but is lower risk because of UV and the volume and mixing of air. But where those things aren’t present outdoors is just like indoors, and very risky when crowded.
@DavidM_yeg I believe your understanding of UV radiation from the sun is incorrect. I've seen several articles that indicated UVC rays can kill COVID, but that doesn't penetrate the atmosphere. The UV rays that reach us do not seem to impact COVID.
https://www.aad.org/public/diseases/coronavirus/can-sunlight-kill-coronavirus
Interesting… thanks for that, I’ll do some more digging!
I’ve read through what you linked and noticed the following:
- they focus on countering the idea that UV exposure (sunbathing) cures or prevents Covid
- they both warn that UV radiation generally can be harmful to humans
- that each say that UVC is more effective than UVB or UVA, not that the others have no effect
Neither addresses whether ambient outdoor UV impacts the risk of transmission.
1/
I find it very difficult to find good information about the effects of ambient UVA, UVB, because most studies point to UVC as the most effective for disinfection/sterilization and disregard effects on transmissibility.
There are number of studies that have identified an inverse correlation between the UV Index and Covid morbidity and mortality in the following time periods. The mechanisms posited include direct effects and increased vitamin D production.
@DavidM_yeg @augieray I did immediately bump into this paper where the authors claim "to show that (a) UV-B/A photons have a powerful virucidal effect on the single-stranded RNA virus Covid-19 and that (b) the Solar radiation that reaches temperate regions of the Earth at noon during summers, is sufficient to inactivate 63% of virions in open-space concentrations ... in less than 2 min.'
https://www.nature.com/articles/s41598-021-94417-9
Of course that's just one paper, it's old (relative to the amount of time COVID has been around), I'm only going based on the abstract, and this isn't remotely my field, so I'm not vouching for that claim or the paper in general.
@internic @augieray
Thanks for sharing this, Nick. Reassuring (sort of) to hear the authors observe that there is relatively little research on the topic … at least I’m not missing something obvious. What they find suggests that the role I thought UVA, UVB might play in the risk reduction of outdoors might hold up.