By Dr. Alondra Nelson
The most common way COVID-19 is transmitted from one person to another is through tiny airborne particles of the virus hanging in indoor air for minutes or hours after an infected person has been there. While there are various strategies for avoiding breathing that air – from remote work to masking – we can and should talk more about how to make indoor environments safer by filtering or cleaning air.
In fact, research shows changing the air in a room multiple times an hour with filtered or clean outdoor air – using a window fan, by using higher MERV filters in an Heating, Ventilation, and Air Conditioning (HVAC) system, using portable air cleaning devices, and even just opening a window – can reduce the risk of COVID-19 transmission – with studies showing five air changes an hour reduce transmission risk by 50 percent. 1,2 And, improving indoor air has benefits beyond COVID-19: it will reduce the risk of getting the flu, a common cold, or other diseases spread by air, and lead to better overall health outcomes.
The Biden-Harris Administration identified improved indoor air quality as an important tool to fight the spread of airborne diseases in the American Pandemic Preparedness Plan last September – and the National COVID-19 Preparedness Plan prioritized it again earlier this month. A number of Federal departments and agencies – including the White House Office of Science and Technology Policy (OSTP) – have worked together to launch the Clean Air in Buildings Challenge, a call to action for anyone who manages or maintains a building. As part of the launch, the Environmental Protection Agency released a practical guide for building managers, contractors, homeowners, and business owners to create an action plan for cleaner indoor air.
Now, we all need to work collectively to make our friends, family, neighbors, and coworkers aware of what we can do or ask for to make being indoors together safer. Each of us has a set of simple but powerful actions we can use to bring clean air into the rooms we’re in and clean the air already in the room.
Here are the basics:
- Ventilation: Bringing in clean outdoor air is key. Indoor air moves less than outdoor air, so virus particles hang in the air in greater concentrations. Ventilation strategies that bring in more outdoor air can disperse viral particles and lower the risk of people inhaling them or getting infected through their eyes, nose, or mouth. Fans and HVAC systems can help make open windows more effective by pulling in clean outdoor air, and can send clean air into rooms without windows or good ventilation. New buildings are often constructed to seal air in for energy efficiency, so their HVAC systems must be on or their windows opened to clear the air. Older buildings may be less well sealed, but have outdated air handling systems or lack them altogether. An HVAC expert can help with this; more resources are available here.
- Air filtration: Using high-quality air filters like HEPA or MERV-13 – connected to capable HVAC systems or portable air purifiers – to remove virus particles from indoor air is also important. Filtration is a great tool to supplement ventilation or to use if adequate ventilation isn’t possible – for example, if extreme temperatures, wildfire smoke, or outdoor pollution make you not want to open a window. And we need filtration equipment more than we might think: many schools, workplaces, hotels, and homes have windows that do not open at all. Many Americans and small businesses cannot afford major HVAC upgrades. While all of us can benefit, many Americans have health vulnerabilities and need the extra protection of having cleaner air. In all these cases, portable air cleaning devices with powerful fans – as powerful as a box fan you could buy at a store – can make a big difference in reducing virus particles in the air. HEPA filters, for instance, are at least 99.97% efficient at capturing human-generated viral particles associated with COVID-19. As a temporary measure, there are affordable and effective DIY options, including the four-filter-plus-box-fan cube called the Corsi-Rosenthal box.
- Air disinfection: By inactivating (“killing”) airborne virus through methods like ultraviolet germicidal irradiation (UVGI) systems, we can add another layer of protection in indoor spaces. The latest technology in these UV lights is particularly useful in crowded areas with poor airflow, in healthcare settings with vulnerable populations (such as hospitals or nursing homes), or in areas like restaurants where people aren’t wearing masks because they’re eating and drinking. For instance, one study demonstrated that when used with proper ventilation, UVGI is about 80% effective against the spread of airborne tuberculosis, equivalent to replacing the air in an indoor room up to 24 times in an hour.  However, there are some challenges to doing this widely, and more research and innovation is needed to develop UVGI systems that are more affordable, standardized, and consume less energy.
Used along with layered prevention strategies recommended by Centers for Disease Control and Prevention and others, improving indoor air quality is a critical part of a plan to better protect us all. But it will not by itself eliminate the risk of infection: the best way to protect yourself against COVID-19 is to get vaccinated and boosted.
For decades, Americans have demanded that clean water flow from our taps and pollution limits be placed on our smokestacks and tailpipes. It is time for healthy and clean indoor air to also become an expectation for us all. Clean and healthy indoor air is a fundamental commitment we must make to our children, to workers, to those who are medically vulnerable, and to every person in the country.
Now we’re making it possible: Federal funds and resources are available to support improvements in ventilation, filtration, and clean indoor air – the American Rescue Plan has $122 billion for schools and $350 billion for state, local, and Tribal governments, which can support upgrades to their local businesses, nonprofits, community centers, and other commercial and public establishments. Additionally, the Bipartisan Infrastructure Law provides billions of dollars to our communities to support people’s health and safety in new or upgraded airports, transportation hubs, low-income housing, schools, and other buildings.
Scientific and public health evidence supports practical, actionable solutions for cleaner indoor air. It is time for a national conversation on how better indoor air quality can help us all live healthier lives.
 Rothamer, D.A., et al. Strategies to minimize SARS-CoV-2 transmission in classroom settings: combined impacts of ventilation and mask effective filtration efficiency. Science and Technology for the Built Environment, 27:9, 1181-1203 (2021). https://www.tandfonline.com/doi/full/10.1080/23744731.2021.1944665
 de Oliveira, P.M., et al. Evolution of spray and aerosol from respiratory releases: theoretical estimates for insight on viral transmission. Proceedings of the Royal Society A 477: 20200584 (2021). https://doi.org/10.1098/rspa.2020.0584
 Mphaphlele, Matsie et al. Institutional Tuberculosis Transmission. Controlled Trial of Upper Room Ultraviolet Air Disinfection: A Basis for New Dosing Guidelines. American J Respir Crit Care Med, 192(4), 477-4848 (2015). https://doi.org/10.1164/rccm.201501-0060OC
Dr. Alondra Nelson is head of the White House Office of Science and Technology Policy and Deputy Assistant to the President.
Adapted from the original with modest edits to remove an outdated event. A useful resource is the COVID is Airborne website.
Public health coverage in the magazine is supported by a grant from the Marion County Public Health Department.