What Is the Risk of Catching BA.5 Outdoors?

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Ahead of a large music festival in Ottawa, Ontario, this past weekend, the city’s public-health agency, faced with a wave of new COVID cases, advised wearing a face mask at crowded outdoor gatherings. Such advisories have not been common, but that doesn’t mean it was bad advice.

COVID is everywhere again thanks to a large and growing ongoing surge of new infections and reinfections fueled by more transmissible Omicron subvariants, particularly the extra-worrisome and now-dominant BA.5 strain that is equipped with more immune escape than any of its predecessors. As is always the case, one of the best ways to avoid being exposed to COVID is to avoid crowded indoor spaces — especially those with poor ventilation — or, at the very least, wear a tightly fit high-filtration face mask (like an N95, KF94, or KN95) in such places. But is there now an increased risk outdoors as well?

Simply put, the risk of catching COVID is always lower outside — and usually significantly lower — since outdoor spaces naturally provide far more ventilation and typically allow more room to space out from other people, both of which make it harder for the virus to successfully travel from one person to another. But outdoor activity has never been zero risk when it comes to avoiding COVID, and there are, of course, variables that increase that risk. The good news is that most of them are simple to understand and mitigate by using some common sense.

Most important, any factor that affects the risk of exposure and transmission indoors also applies outdoors. Being in a big tightly packed crowd outside, like at a music festival, means more risk. Hanging out in a crowded, enclosed outdoor space, such as a wedding tent with the side flaps down? More risk. Mixing it up at a jammed patio bar when there are high levels of COVID in your community? More risk. And, of course, as computational epidemiologist Maimuna Majumder recently noted to NPR, “The more transmissible a variant is indoors, the more transmissible it is in outdoor settings, too.” And particularly since it will likely take less exposure, or for a shorter amount of time, to catch COVID from someone else infected with a more transmissible variant.

“The risk outside is going to be substantially less than inside but we don’t know if it’s changed because we haven’t had a lot of experience with BA.4 and BA.5,” UC Berkeley infectious disease expert Dr. John Swartzberg told the San Francisco Chronicle last week.

“I think big crowds, even outdoors, can pose a serious risk right now with test positivity in double digits in many big cities,” explained Stanford infectious-diseases doctor Abraar Karan in an email, but he also stressed that the same interventions that work against indoor transmission, like wearing a high-filtration mask, will protect you outside.

That doesn’t mean everybody should consider masking up all the time outside or even most of the time. But it does mean that having a good mask handy, keeping an eye on how many people you’re around, being careful when outdoor events shift indoors — and adjusting your behavior and level of precaution as needed — remain good ways to avoid infection and reinfection regardless of where you are, whom you’re around, or what scary subvariant is making headlines.

What Is the Risk of Catching BA.5 Outdoors?