Can Air Purifiers Save Us From COVID-19?

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In a world that’s desperate for a solution to coronavirus, most of us will cling to any glimmer of hope — anything that will decrease our chances, even a little bit, of catching the deadly virus that causes COVID-19. And lately, people have been obsessing over the idea that Air Purifiers with HEPA filtration might protect them against infections.
Interest peaked after New York Governor Andrew Cuomo announced last week that malls in his state wouldn’t be allowed to reopen until they installed HEPA (short for "high efficiency particulate air") air filters. But before you run out and buy one of the pricey home filtration systems, know that it’s not a failsafe way to prevent SARS-CoV-2, says Jill Grimes, MD, a family physician in Texas. It shouldn’t be your first — and certainly not your only — line of defense. No filter will be a substitute for wearing a mask and social distancing, the two most effective ways we know of to combat catching the disease. “You can think of an air purifier as an extra layer of protection, but it won't make you bulletproof,” Grimes says. “You might have a HEPA filter in your office, but that doesn’t mean you don’t wear a face covering.” 
That’s because the Public Health Agency of Canada says that “current evidence suggests person-to-person spread is efficient when there is close contact." Yes, it may also be transmitted in other ways, and it’s great to protect yourself against those, too, but the bulk of the transmission is happening when you’re breathing in the respiratory droplets of others. Buying a HEPA air filter but not wearing a mask would be like installing a high tech adaptive cruise control system in your car, but not wearing a seatbelt. 
The spike in HEPA fascination comes after more than 200 scientists wrote an open letter in early July to the World Health Organization and other health agencies requesting they “recognize the potential for airborne spread of COVID-19.” Since the letter, WHO updated its guidelines on July 9, acknowledging there have been outbreaks in closed settings such as restaurants, nightclubs, and churches where aerosol transmission “cannot be ruled out.” Although coronavirus is most widely known to spread through droplets produced when someone coughs, talks, or sneezes, the idea that teeny tiny droplets (droplettes, if you will, that are officially called aerosolized droplet nuclei or “aerosols”) may also spread it is being investigated. We also already know that some medical procedures can produce these aerosols, which will stay in the air for a while, Dr. Grimes says. 
One solution to the aerosol quandary is to stay outdoors when you interact with folks outside of your bubble, says Paul Pottinger, MD, a professor specializing in infectious disease at the University of Washington School of Medicine. “We have enough information now to tell us that it’s better to interact with others outside where there’s more air circulation,” Dr. Pottinger says. He worries that folks will assume that it’s OK to hang with larger groups indoors or go to the mall without a mask, just because they have an air filtration system. 
“I’m concerned that things like HEPA filters are going to take us off message — air purifiers and UV light are all secondary, and much, much less important than everyone following the rules, social distancing, and covering their damn face,” Dr. Pottinger cautions. “If everyone does that, all these expensive, high-tech, pie in the sky, not-gonna-happen-on-a-large-scale solutions — they just won’t be necessary.” 
Still, Dr. Grimes says she’ll probably buy an air purifier for her child’s dorm room this year, where it will serve as one of many prevention tools her daughter will be able to utilize.
So, what's the deal — should you buy one? Here’s what you need to know right now about filtration systems and how much of a difference they might make.

What even is HEPA?

This technology uses a fan to draw in particles that are in the air and capture them. The mechanical filters can remove at least 99.97% of mould, pollens, dust, bacterias, and airborne particles, according to the U.S. Environmental Protection Agency.  Some units can be as cheap as $50, while other fancier versions can be over $600
These filtration systems are often recommended for folks with allergies, Dr. Grimes says. She recommends looking into the details before you buy them, as some are designed for larger rooms and some are for smaller ones. That will make a difference in effectiveness, whether you’re trying to filter for allergies or potential coronavirus aerosols. 

Do HEPA filters kill COVID-19? 

The virus which causes COVID-19 is about .125 micron, a size of particle that HEPA filters can capture effectively, The New York Times notes. HEPA technology can handle 0.01 micron and above, according to a NASA study on filtration. 
Some experts say that because of this, “healthy buildings” with good ventilation and filtration systems should become the norm. Of course, scientists still don’t know for sure what level of exposure to the coronavirus will cause an actual infection.
"The prudent and pragmatic approach is to acknowledge that airborne transmission is happening and put in the controls,” Joseph Gardner Allen, director of the the Healthy Buildings program at the Harvard T.H. Chan School of Public Health, told CNN. “If we find out in five years, that airborne was 5% of transmission, then OK… But what if it's 20% or 30% and we failed to acknowledge it? That's a problem."
On the flip side, researchers don’t know if HEPA filters have the capability to rid the air of possible viruses before someone gets infected. “The challenge is, if someone is in the room with you and they have COVID, they’re continuously reintroducing the virus into the air,” Dr. Grimes says. “It's similar to if your window was open and pollen kept coming in." They can’t do the job effectively if they keep getting blasted with new toxins.

So, should I pony up for an air purifier

If it’s in your budget, especially if you already suffer from allergies, it could be a decent buy. If you’ll be in a dorm or an apartment where you worry about breathing in uninvited aerosols, Dr. Grimes says it could also be a worthwhile investment. But both Dr. Pottinger and Dr. Grimes say budgeting for face masks should be your first priority. “Think of a mask as your own personalized HEPA filter for your face,” Dr. Grimes says. 
Dr. Pottinger adds: “How far the virus will spread in buildings versus outdoors is interesting, but it will not change the fundamental truth that you’ve got to cover your face.” 

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