Covid & Airborne-Virus Prevention Tips
Last Updated: Jan 2, 2025
Cases are on the upswing again, so it’s a good time to think about upping those precautions as the 10th wave hits and H5N1 ramps up!
Here’s a list of my covid-prevention tips (which work for all airborne viruses!), in order of estimated effectiveness. Do as many as you can, the “Swiss Cheese” approach works better than relying on any one single precaution. Also viral load matters, so even “failed” precautions will still likely result in less illness for you and will reduce your risk of Long Covid.[1]
It’s also important to remember that covid is AIRBORNE, so all the hand-washing/hand sanitizer in the world won’t help prevent it (though hand-washing can prevent other viruses, so obviously still a good idea). As far as we know, there are no cases of fomite transmission for covid (where aerosol transmission cannot be ruled out).[2] Infection with covid and other airborne illnesses is via breathing viral aerosols through your mouth and nose, so to avoid it you need to focus on preventing breathing it in.
RESPIRATOR-STYLE (KN95/N95/P100/ELASTOMERIC) MASKS
Most folks don’t want to hear it, but the single most effective precaution we can take to stop breathing in viruses is by covering our mouth and nose with a filter to trap the viral particles—so masking, especially indoors, or outdoors in crowds or near people exercising or singing (exercise and singing greatly increase the number of aerosols expelled[3], [4]).
An n95 (headstraps) with a good seal is about 95% effective, hence the name (more if you can do a fit test / fit testing kit and guide). A kn95 (earloops) is about 85% effective.
If you can’t do a fit test, do a seal check. Small changes like adjusting the nose wire can improve your mask seal significantly. (note: a seal check is not a replacement for a fit test)[5]
Here’s a great video about how n95s work: The Astounding Physics of N95 Masks
If you want even more protection, P100s and reusable elastomeric respirators are nearly 100% effective when fit-tested and many people find them more comfortable, better for the environment, and often cheaper in the long run.[6]
Surgical and cloth masks have *some* efficacy[7] but I wouldn’t wear those anymore unless there’s no other choice. They are better than nothing (and work better as source control) but if you can, please wear a kn95 or n95 or better (Note: there are many many kn95s with lots of fun colors and patterns if that is desired—the Still Coviding In Style fb group is my favorite resource for these).
If cost is a concern, you can absolutely rotate and reuse kn95s/n95s until they get wet (some liquids can destroy the electrostatic charge),[8] get dirty, or until about 40 hours of wear. There are also mask blocs around the country providing free masks (please donate to your local mask bloc if you are able!). There are often sales at the big sellers (maskc, poshmask, wellbefore, etc). You can also buy and use expired masks, there appears to be very little decrease in efficacy, even after 10+ years.[9] Also, call your representatives and ask for free n95 masks—there is a bill being considered at the NYC City Council, please call to support (or your local reps if you aren’t in NYC)!
If you need help choosing a mask, I recommend a 3M Aura to start, which will pass a fit test on approximately 85% of folks.[10] There is a guy called the MaskNerd who ranks masks and efficiency. He has a master spreadsheet here: Master Mask Testing Data Set
The Masks4All subreddit would LOVE to help you choose a mask. For hard to fit faces (including toddlers!) I really like the Zimi mask which comes in multiple sizes (https://zimiair.com/).
If you’re traveling or going to a bar/concert/party and will need to drink something but don’t want to risk taking off your mask (a good idea), I highly recommend the Sip Mask valve, which can be installed on almost any kn95/n95 mask and doesn’t decrease mask efficacy. You can also eat Pocky cookies through a sip mask.
AIR QUALITY
Outdoors is Safer:
We all know that outdoors is lower-risk (nearly 19 times safer[11]) than indoors (but not no risk!), so hang out outdoors whenever possible. Prepare for an outdoor hang by dressing/planning appropriately—In Norway, they say there is no bad weather, only bad clothing! (In winter, I’ve been more comfortable with merino wool underlayers, hot hands, a wool hat & socks, and warm beverages & a fire pit/outdoor heater. In summer, a good hat, a spray fan, and ice packs and cool drinks go a long way!) Here’s a crowd-sourced map of outdoor restaurants in NYC.
If you must be indoors, increasing the air quality of your indoor space by opening windows, running ceiling fans,[12] and running air filters and/or far UV, will greatly decrease the likelihood of anyone getting sick (30-85% reduction, depending on the study and the air quality improvements).[13]
Air Filters:
Air filters can ensure that the filtered air you're breathing (that was just in someone else's lungs!) is at least virus-free (they work the same way as a mask, by trapping viral particles in a filter). The more air filters in the space, the better—in fact, several air filters are actually MORE effective than one large one, as they capture germs from multiple areas in a room, making it more likely that the air you are breathing is clean. Place the filters as close to the center of the room as you can or evenly spaced if you have multiple purifiers, with the fan ideally placed at the same height as the occupant’s heads, and run on the highest possible setting.
I like this site for air filter reviews:
https://housefresh.com/air-purifiers/
This is also a great air filter recommendation tool:
https://cleanairstars.com/filters/
Personally, I recommend the AirFanta 3 Pro (the cheapest CADR for the price, also great for traveling or taking to events as it fits in a carry on!) and the Levoit Core 600s and 400s because you can program a schedule for them with your phone. If noise is an issue, the Tempest or Clean Air Kits are nearly silent and are your best options (though you need to be somewhat handy to put them together). Avoid air filters with ionizers.
The CDC recommends a minimum of 5 ACH (Air Changes per Hour).[14] The more, the better though!—most hospitals have at least 12. If you’re high-risk or living with someone who is, I would aim for 12 in your main shared living space. Here’s a tool to calculate air changes if you have the cadr (clean air delivery rate) of your air filter (usually this is available on the documentation that comes with the purifier or on the housefresh.com site, or you can look it up here)
If you can’t personally control the air quality of a space, or don’t know if there will be plugs available, there are small battery-operated portable air purifiers you can bring with you, but their effectiveness varies WILDLY. Making your own is probably the most effective (instructions here—my kids and I carry these around with us everywhere in mesh sling bags with VitaLights clipped to them), and here’s a roundup of commercial mini purifiers from HouseFresh. You can also check out the laminar AirFanta 4Lite. Note that no personal filter will clean the air enough to unmask safely, so it’s very important you have additional Swiss Cheese layers in place.
CO2 Levels:
A good way to tell if a space has good air quality is to use a CO2 (carbon dioxide) monitor. That will tell you if the building’s HVAC system is working well or poorly. Note: if you are using air filters to add additional air changes, they clean the air but don’t remove CO2, so the readings won’t improve. It’s still a good idea to remove high CO2 even with air purifiers running.
Here’s a great short video from public health expert Dr. Lucky Tran explaining CO2 Monitors: https://x.com/luckytran/status/1809633702588067881
High CO2 makes viruses easier to spread,[15] and can cause all sorts of cognitive problems, including headaches, drowsiness, irritability, trouble concentrating,[16] and, if you are unlucky enough to be sharing a room with someone contagious, it means you are rebreathing the air that was just in their lungs, making it increasingly likely that you will get sick with each and every breath you take. When you’re in a car and you feel very sleepy, it’s likely because the CO2 levels are too high (always have your car air on fresh air, never recirculate), which is why opening a window helps almost immediately.
Ideally, the CO2 levels would be under 800 (outside air is around 425). If levels are high, open windows and/or doors to let some of the CO2 out. (even cracking a window, especially when it’s cold out, will allow CO2 to escape. Better a crack than nothing at all).
To monitor CO2 you need a CO2 monitor! The gold standard is the Aranet, which you can link to an app and see historical data which is quite helpful. However, it’s pricey, so for a budget option I recommend the VitaLight. I like the Vitalight because it has an optional alarm feature that will alert me when levels are too high so I can open a window if possible (or leave). It’s also easier to get other people to help with air quality changes when you have a device beeping.
You can look up recorded CO2 levels for indoor locations on the website co2trackers.com — and you can also add more data if you have it (right now most of the users are in NYC so many of the readings are there). Please add readings if you can! It’s helpful to see if a space has bad or good ventilation. Before outings, I always try to check out that site to get an idea about the air quality.
Far-UV Lights:
We all know that UVC light kills viruses and bacteria, but it’s unsafe for humans to be directly exposed to it. However, there is a narrow band of light called Far UVC (222nm) that is safe for human exposure.[17] UV lights can kill far more germs than air filters alone.[18] If you have the funds, I recommend this farUV torch set, which is easily portable. Lots more info on the science on their website as well:
https://cybernightmarket.com/products/mini-far-uvc-lights-set / https://www.nukit222.com/
For a permanent installation, the Beacon is popular.
A deeper dive on Far UV from Jessica Wildfire.
Right now, FarUV is pricey, but like most new technology, I anticipate prices will drop with more widespread use.
ORAL PROBIOTICS or CPC MOUTHWASH (one or the other, not both)
There’s a probiotic strain called Blis K12 that has shown stunningly good results in studies for preventing infections of all kinds, including covid.[19] Apparently, the good bacteria populate your mouth & nose after about 2 weeks (10 days if using 2x a day) and make the environment inhospitable to viruses. Studies show up to a 80% reduction in viral infections.[20] And they’re safe for kids. Note: they contain dairy so might be an issue if you are lactose intolerant. You can purchase them here:
https://www.amazon.com/BLIS-ThroatHealth-Probiotic-Available-Sugar-Free/dp/B077X6N5KS/
The Blis team recommends mouthwash at a max of 1x per week and waiting 30 minutes after mouthwash before using a Blis lozenge.[21]
If you aren’t using Blis K12, to prevent infections it’s recommended to gargle with CPC (Cetylpyridinium Chloride) mouthwash at least once a day. (Most mouthwashes contain CPC: Act, Crest, Colgate etc. Listerine has also been shown to kill covid in vitro but doesn’t have CPC.[22] Note: CPC can stain teeth in rare cases). CPC can kill viruses hanging out in your mouth and throat,[23] however, they will also kill the good bacteria that BlisK12 provides, so you basically have to choose one or the other. The studies are more encouraging on the Blis, so personally I would pick that. But if you are not taking Blis and go to a higher-risk event, definitely gargle with mouthwash as soon as you get home. If you are sick, gargle with mouthwash 2-4 x/day.
PRE-EVENT RAPID TESTING/SCREENING
Before hanging out with folks, it’s a good idea to ask them if they’re feeling off or sick, or had any recent covid exposures. It’s easy to mistake the start of an infection for allergies, so if someone says they have allergies or are feeling off, I definitely would think twice before getting together (and at a minimum make them test negative and hang out outside). Note that more than 55% of covid infections are spread either pre-symptomatically (more than 40%) or asymptomatically (15%),[24] so a lack of symptoms doesn’t mean someone doesn’t have covid. If someone has recently had covid, make sure they have tested negative on 2 rapid tests 48 hours apart before spending time with them.
If you can get everyone to test, a RAT (Rapid Antigen Test) is about 50% effective at ruling out covid depending on how far into an infection you test (not great, but still a decent reduction in risk. FlowFlex seems to be the most accurate RAT). The rapid tests are really designed to be used serially 48 hours apart,[25] so using the tests in that fashion would make me more confident in the result.
The best quick testing option is a NAAT (Nucleic Acid Amplification Test)—they are much more accurate than a RAT. More info about NAATs from Clean Air Club. They’re pricey though. :( If someone has access to a PCR(polymerase chain reaction) test (there is one free location left in Brooklyn in Crown Heights) that would be the best option, as long as they didn’t do anything risky after taking the test.
RATs (including FlowFlex) are significantly cheaper in the UK and Europe ($1-2 each) if you know someone coming back from there—I have stocked up by asking friends to bring them back for me from their trips. Also please call your city council member/local reps, as there’s a bill to provide free tests in NYC again, which should just be a thing.
NASAL IRRIGATION/SINUS RINSE/NETI POT
Your nose is where airborne viruses multiply before invading the rest of your body.[26] Several studies show rinsing your nose to reduce the amount of virus can shorten the duration of an infection[27] or even prevent it entirely.[28] In one study, healthcare workers who masked in n95s and rinsed daily after their shifts in covid wards had a 1% chance of catching covid, significantly less than the workers who relied solely on their masks.[29]
I use a neti pot/sinus rinse bottle (I like the Squeezie) with saline packets (they come with the kit or you can make your own with salt & baking soda) and distilled or boiled-then-cooled water (never use water direct from the tap). Make sure the water goes in one nostril and out the other (it feels a bit like going swimming, it’s not at all scary, I promise!). I like heating the distilled water in the microwave for approximately 10-15 seconds to make the rinse more comfortable. Also great for kids!
Pediatric Nasal Rinse - How a Sinus Rinse is Performed in Kids!
I recommend sinus rinsing as soon as possible after a high risk event, especially if unmasked. Follow up after your nasal irrigation with your nasal spray of choice to hopefully kill any remaining germs in your nose. If infected with something, or if you have an exposure, rinse 2-4x day.
More info on nasal irrigation from Clean Air Club.
NASAL SPRAYS
There’s lots of early evidence that nasal sprays can help prevent infections and lessen the duration of illnesses if used when infected[30] by disrupting the viral particles from replicating in your nose.
For kids and pregnancies, I recommend Xlear, as it’s the only brand that’s safe for littles (please keep away from pets).
For everyone else, there are a ton of different brands. Everyone has their own preference (if you search social media you will get a LOT of opinions), but popular options include Covixyl, Profi, Enovid, and Xlear[31]. They are most effective in conjunction with masks (but again, something is better than nothing if you can’t mask). If price is a concern, generic Xlear/xylitol spray is the cheapest option. More info on nasal spray options from Chicago’s Clean Air Club. and from Jessica Wildfire.
I recommend using a nasal spray immediately before a potential exposure and again just after leaving, and 3-4x a day if you are battling off an infection.
VACCINES
We all know that the mRNA vaccines reduce severe symptoms, but their efficacy in preventing infections entirely has severely waned, due to the fast mutation rate of the virus.[32] They also don’t create strong antibodies in our noses,[33] which is what we would need to get sterilizing immunity. The mRNA vaccines wane quickly—in March 2024, the fall 2023 boosters were less than 19% effective.[34] If you have an option, there is some early evidence that the protein-based (mRNA-free) Novavax (and right now only Novavax) can produce some mucosal (nasal) antibodies after 3-4 shots.[35] Personally, I plan on getting Novavax every 6 months from now on, if I can. Again, though, any vaccine is better than no vaccine for most people, but please don’t count on them preventing infection, especially if you are more than 6–8 weeks out from a shot. Ideally, you would have many layers of Swiss Cheese in place before your vaccine would be necessary as a last resort.
THANK YOU
Thanks so much to all the folks sharing their wisdom and tips, (mostly on twitter!) who have turned me on to all this data.