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Omicron FAQ: How long does COVID-19 last in a room? Can cloth masks be safer? Can I reuse an N95 mask?

Damian Dovarganes
AP Photo
A Metro Transit bus driver wears an N95 protective mask and gloves as she drives her bus near Staples Center in downtown Los Angeles, Monday, Jan. 25, 2021.

It’s normal to be overwhelmed or anxious about doing anything as the pandemic continues to wear on and scientists and epidemiologists learn new information about COVID-19, resulting in continually updated guidance.

Much of that guidance revolves around what we now know about the omicron variant, which is behind recent surges throughout the U.S.. Sacramento County broke its record of hospitalizations during Martin Luther King Jr. weekend, with 570 people in the county hospitalized with COVID-19 as of Jan. 17, more than the 518 reported on Dec. 20, 2020 during the pandemic’s initial winter surge.

The omicron variant was first identified in November, and by December it overtook the delta variant as the culprit behind the majority of COVID-19 cases in the country.

“It is notoriously good — and probably one of the most efficient viruses many people have seen, at least in their lifetime — at moving person to person,” said Dr. Kirsten Bibbins-Domingo, chair of the UC San Francisco department of epidemiology and biostatistics. She also heads up the UC San Francisco COVID-19 Community Public Health Initiative.

Bibbons-Domingo spoke with CapRadio about what we know now about how COVID-19 — specifically the omicron variant — spreads, which masks can best protect against the virus, and other questions to think about as we try and stay safe in this latest wave.

She also discussed her approach to deciding what activities are safe to her during the omicron surge here.

This interview was edited for length and clarity. 

What have we learned about how COVID-19 spreads since the start of the pandemic? Why is omicron spreading so quickly? 

COVID is a virus that spreads in the air. One of the reasons we think that omicron is more infectious and moves more easily from person to person is it seems to be preferentially in your nose and mouth and upper airways. It seems to not like to spread in the cells that are deep in your lungs. Both are probably the reasons it is a little bit better at getting out across from one person to another.

Because it's not as much in the lungs, [that] may be the reason [that] for many people, it doesn't cause as severe pneumonia and the things that land you in the hospital. … But it is notoriously good — and probably one of the most efficient viruses many people have seen, at least in their lifetime — at moving person to person, because it spreads through the air.

At the start of the pandemic, when we knew very little about the virus, we were particularly concerned that we had to scrub the pizza boxes when they were delivered to our houses, or that if someone [who tested positive] had touched something, that we had to be worried about touching that surface. That is probably not a very useful way to think about the virus. What is much more useful is to think about those droplets from people who are positive, or the very fine droplets that hang in the air in rooms that aren't ventilated.

I think that way of thinking about the virus is helpful, because it helps you to understand why masks are way more important than just sanitizing surfaces. It also makes all of us understand that what we can do to help is not just the things that we do individually, but the things that we do to our rooms and our buildings and our spaces to keep them safer. It has to have very much to do with ventilation.

How long can COVID-19 droplets stay in a room?

In general, these [COVID-19 droplets] are not droplets that are staying in the air for extraordinarily long periods of time. But part of the reason why we are concerned about rooms that aren't ventilated, and we know ventilation is important, is that we should think of these as very fine droplets that do hang in the air for a period of time.

I'm generally not as concerned that, you know, something that happened in the room half an hour ago is going to be a risk to me. But if I were in an environment that really has no circulation … you can't ever be quite sure.

I don't get nervous, when I go into a room, about who's been in the room before me.

But I do get nervous anytime I'm inside a room that's not that well-ventilated, about even people who are across the room, or people who might be much further from me than I would generally think about. Because the air that's there is just not circulating in the way that is really designed to keep me safe. Those viral particles are sort of hanging in the air.

What’s the likelihood of COVID-19 coming in through car or apartment vents?

I don't think this is a high area that would personally cause me a lot of anxiety. I think we want to be in the most ventilated spaces possible and in air that is constantly circulating.

I have one of these very modern office buildings, a very large office building that has a lot of open air space, but very little ventilation from the outside. The main thing that we did to improve ventilation was to actually have air come in from the outside, to recirculate the air. What I've come to trust is those people who have just documented over time, how important the ventilation of buildings are, how important the masks are, how the additional things like HEPA filters.

For any given person, tracking down how they got a virus is actually notoriously difficult. When you've heard of these anecdotal cases of concern that there might be something's coming in through the vents, they're really in the context of places that are not recirculating the air. It's not coming in from the outside, it's an event that is not actually circulating new air into a building, air is just sitting more stagnant in there.

How can people make their cloth masks safer, if they can’t get access to N95s or surgical masks?

It's hard to make the cloth masks safer, to be perfectly honest with you.

If I think of a spectrum, what I would love to have [for] the person who wants to be the most cautious, or the person who I'm most worried would have something bad happen to them if they contracted omicron, I definitely want them to have an N95. In the absence of that, I would worry about them spending extended periods of time with other people, at a time when community transmission is as high as it is right now.

After that, the way to improve the surgical mask, where you have some filtration, is to actually improve the fit. What we've advised in case people don’t have access [to a N95] is to wear a cloth mask over a surgical mask because it fits tighter to the face, plus you get some of the filtration benefits of the surgical mask.

If you really can't find either of those categories of things that are optimal for filtration, probably what I would do is double the cloth masks.

But you should recognize that with omicron there, if you're spending any more than a few minutes with people you don't know who might be infected, the cloth mask just isn't enough of a barrier.

Would you wear a cloth mask over no mask?


But I think in this environment of omicron, I think one really has to say, that's the two things that really keep one safe: Covering your nose and mouth and things related to filtering the air. That is what surgical masks and N95s do. And with the fit of the mask to your face, that is what the N95 can do far better than the surgical masks.

Can I reuse an N95 mask?

I would want to emphasize that we can reuse these N95s, so if you find them, you don't have to just throw them away after one use. You can keep them as long as they're clean.

It's important that we talk about omicron, that we're in what is very likely to be a limited surge, a surge that will take place over the next many weeks. Right now, while there's so much omicron in the air, if your goal is to try to really reduce your likelihood of getting omicron, you really want to have the best masks possible.

Even if it's hard to find, I wouldn't give up the effort. If I could find a box and keep it around to use in the riskiest times, that's what I would do, especially as we get to come down off this peak, which will likely be at the end of January, going into February.

This guide has more on how to select a N95 mask that fits you best, including where to buy one and make sure it isn’t a fake.

You can find free community walk-up testing sites in Sacramento here and order your four free COVID-19 tests (one order per household) from the U.S. Postal Service here.