As winter nears, more people will be spending time with others indoors, a scenario that favors high coronavirus transmission. On top of mask wearing and social distancing, experts say investing in air filters can be a helpful addition to infection prevention plans.
But there’s one point to keep in mind: “Air purifiers [with filters] are not a magic bullet. So, it’s important to think of them more as part of your plan rather than your whole plan,” said Tim Peglow, vice president of Patient Care and Patient Facilities at the University of Texas MD Anderson Cancer Center.
There still lacks significant evidence that air filtration works to reduce the spread of COVID-19, but experts agree the potential benefits outweigh the cost.
The most common type of home air filters are HEPA filters, which stands for “high-efficiency particulate arresting.” They work by grabbing and trapping particles from the air onto the filter itself, preventing them from breaking free and recirculating.
This means HEPA filters don’t kill the virus, but instead they clean the air rapidly and get rid of it.
The filters are designed to remove 99.97% of airborne particles as small as 0.3 microns in diameter, or about a fraction of the width of a human hair, experts told NPR.
Although the coronavirus is about 0.1 microns in size, the pathogen does not travel alone — and will die if it does.
“The virus is not expelled on its own. The virus has to attach to something. A microscopic piece of mucus, a piece of dust in the environment ― that’s how it travels,” said Dr. Gregory Poland, a Mayo Clinic infectious diseases expert. “A HEPA filter catches those and holds them there. It does mean that you have to change your filter at appropriate intervals.”
Not much is known about how air filters and the coronavirus interact with each other, but studies on past viruses such as the severe acute respiratory syndrome (SARS) suggest they work to some degree.
“In theory, if an air purifier removes viruses from the air, it reduces concentrations in the room and thus reduces the potential for exposure,” Linsey Marr, an environmental engineer and professor at Virginia Tech who specializes in airborne disease transmission, told Consumer Reports. “So there is a mechanistic reason to think that air purifiers could help reduce transmission.”
There are also some air purifiers that come equipped with ultraviolet light, which can kill some viruses, including SARS-CoV-2, the virus that causes COVID-19.
However, experts warn that air filters shouldn’t replace other preventive measures such as mask wearing and physical distancing.
“Masks offer at least a 50% risk reduction,” said Richard Corsi, dean of the College of Engineering and Computer Science at Portland State University, according to NPR. “A personal air cleaner might reduce that another 50%, for a total risk reduction of 75%. Increased ventilation could get the reduction to 85% or 90%. But if you take off the mask, that percentage plummets.”