- Simple ventilation can reduce infections by 39% .
- Air filtration can reduce infections by 65% .
- Filtration and masks can reduce infections by 90% .
SARS-CoV-2 replicates in the respiratory tract and spreads through the exhalation of infectious respiratory particles. The chances of transmission increase the longer an uninfected person remains in a closed space with an infected person . Infection can occur not only through short-range transmission of exhaled respiratory particles from an infectious person resulting in mucous membrane deposition or inhalation of exhaled respiratory particles from an uninfected person.
Infection can also occur through long-distance transmission by inhalation of infectious respiratory particles that remain suspended in the air for longer periods (potentially after the infectious person is no longer present) and over longer distances ( more than a few meters).
Because no single approach is 100% effective in preventing COVID-19, prevention measures work best when combined , including vaccines and non-pharmacological interventions that reduce inhalation of infectious particles.
Community masking and physical distancing , both of which can reduce the likelihood of encountering and inhaling virus-containing particles, have received considerable attention. However, there is less public awareness of existing indoor air recommendations that can directly reduce the number of virus-containing particles in indoor air and therefore reduce the risk of inhaling these particles from shared air.
Methods to reduce the concentration of SARS-CoV-2 particles in indoor air include ventilation, filtration and disinfection .
Much remains to be learned about the benefits of specific interventions and combinations in different circumstances. However, observational studies and modeling suggest substantial effectiveness for these strategies used alone, in combination, and with other approaches.
For example, in a 2020 study that included 169 Georgia elementary schools, the incidence of COVID-19 was 39% lower in 87 schools that improved ventilation compared to 37 schools that did not (35% lower in 39 schools that improved ventilation through dilution alone [incidence rates, 2.94 vs 4.19 per 500 students enrolled] and 48% lower in 31 schools that improved ventilation through dilution combined with filtration [incidence rates, 2, 22 vs 4.
A simulation model found that filtration with 2 high-efficiency particulate air (HEPA) cleaners alone or in combination with mask use could potentially reduce exposure to infectious particles by approximately 65% or 90% , respectively.
To date, there has been limited and uneven implementation of interventions to prevent the transmission of SARS-CoV-2 by reducing its concentration in the air. A report in Morbidity and Mortality Weekly Report highlights the considerable heterogeneity and inequity that schools report in the deployment of these measures. In this report, based on a nationally representative sample of 420 schools in 2022, low-cost interventions (opening windows and doors) but higher-cost , resource-intensive strategies, such as improving heating, ventilation, were widely used. and air conditioning (HVAC systems) were used much less frequently.
Schools in rural or middle-poverty areas (with 26% to 75% of students eligible for free or reduced-price meals) were the least likely to implement various measures.3 Comparable disproportions are likely to exist in other indoor settings, from homes to businesses and large public spaces such as airports.
Reducing pollutants in shared air by improving air treatment systems in buildings is an attractive and widely effective structural measure that does not require repeated individual actions.
A person can wear a mask, open windows and doors, turn on fans and vents, and use portable air purifiers. Like fluoridation of drinking water to prevent tooth decay and improvements in road and vehicle design to increase road safety, structural interventions that reduce the concentration of SARS-CoV-2 particles in the air can protect more people with less individual effort. Such strategies are increasingly valuable as society learns to coexist with COVID-19 and people return to sharing indoor spaces.
There is a growing list of options for structural interventions to prevent COVID-19 through dilution, filtration and disinfection of shared indoor air. Air handling system upgrades, improvements, or configuration changes can reduce viral particle concentrations by bringing in outside air to dilute potential contaminants. Using air filters with higher Minimum Efficiency Reporting Value (MERV) ratings in HVAC systems can more effectively filter respiratory particles from recirculated air. Commercially available, portable HEPA air purifiers can do the same for a single room without modifying the building’s existing air handling system. These devices may be especially useful in areas used by people at higher risk of having or acquiring COVID-19.
Through the American Rescue Plan, Congress has allocated nearly half a trillion dollars ($350 billion for state, local, and tribal governments and $122 billion for schools), about half of which remains available to support improvements on indoor air quality in small businesses, industrial environments, commercial buildings, low-income housing, transportation hubs and schools.
To ensure maximum benefit is obtained from these resources and to protect the public from ineffective or potentially harmful technologies, the Environmental Protection Agency (EPA) recently issued guidance for building owners and operators as part of the Clean Air Challenge. Agency buildings. 5Guidance from the Centers for Disease Control and Prevention (CDC) also highlights proven interventions to improve ventilation and filtration in buildings. 6 The CDC also provides interactive tools for home and schools to estimate the effects on indoor air quality of simple changes such as opening windows, updating HVAC filters, or using a HEPA air filter.
Balancing effectiveness, equity and feasibility means that the optimal set of interventions will vary depending on the setting and situation.
Many ventilation and filtration improvements can be made at no or low cost (<$100), including opening windows, inspecting and maintaining HVAC systems, and using fans to increase the effectiveness of open windows. Portable HEPA air filters can be added for a few hundred dollars each.
Environmental or safety considerations (e.g., extreme temperatures, risk of falls, crime) may make low-cost interventions, such as opening windows, less feasible in some circumstances. In resource-poor settings , there may be fewer resources to mitigate such concerns (e.g., converting non-openable high-floor windows to openable windows with window guards). Although DIY options are not recommended as permanent solutions, they can be less expensive and, when properly constructed, can be more practical in resource-limited settings than commercial options.
The most expensive are large structural improvements, such as new or updated HVAC systems in public buildings; However, these structural changes more equitably improve indoor air quality for many people simultaneously and may also result in energy savings costs. The CDC, EPA, ASHRAE, and other organizations have voluntary recommendations and guidelines for HVAC systems.
Schools that take advantage of available funds to follow these recommendations can improve the health and safety of all students and employees. Companies that upgrade HVAC systems not only benefit from energy efficiency and future cost savings, but they also make the environment safer for all workers and customers, especially essential workers who may need to interact with a large number of people in the audience.
There are several methods available to evaluate whether improvements are working. Carbon dioxide monitors can provide information on how well an occupied space is ventilated. Airflow measurement devices and tracer gas testing can directly examine ventilation rates. Aerosol sensors can determine the effectiveness of filtration systems.
Improving air quality has the potential to reduce not only SARS-CoV-2 infections, but also infections from other respiratory viruses and bacteria, reactive airway diseases (e.g., asthma) triggered by antigens, pulmonary and cardiovascular injuries from inhalation of harmful respiratory particles (e.g., wildfires, smog) and toxicity from inhalation of volatile organic compounds . There is now a once-in-decades opportunity to make sustained improvements to public and private indoor air quality, reduce the risk of COVID-19, and improve school, workplace, and consumer health and safety.
