Public Schools and Ventilation Strategies That Could Reduce COVID-19 Transmission

Improving indoor ventilation is one of the main strategies for reducing COVID-19 infections, along with vaccination. The SARS-CoV-2 virus is transmitted through infectious aerosols floating in the air so ventilation can reduce the concentration of aerosols and the time that someone might breathe in viral particles. Public health officials have said that ventilation of school buildings could be espeically effective in reducing COVID-19 transmission.

Yet survey results reported in this week’s Morbidity and Mortality Weekly Report showed that more than half of school districts did not report having implemented one of the four main ventilation strategies: maintaining continuous airflow by opening windows, using fans and taking other steps to keep the air supply fresh; upgrading or replacing heating, ventilation and air conditioning systems (HVAC); installation of high-efficiency particulate air (HEPA) filters; or installation of ultraviolet germicidal irradiation (UVGI) devices.

Of those four strategies, continuous airflow is the least expensive, and it was the most commonly used among the 8,410 school districts that did respond to the survey, which was conducted from August-December 2022.

The authors note that there is still federal funding to help school districts improve ventilation. “Public health departments can encourage K-12 school officials to use available funding to improve ventilation and help reduce transmission of respiratory diseases in K-12 settings,” wrote Miguella Mark-Carew, Ph.D., and her colleagues.

Among the four ventilation methods the survey asked about, 50.7% of the school districts reporting using continuous airflow, 33.9% had or were in the process of improving HVAC systems, 28% had installed or were planning to install HEPA filtration systems and 8.2% had installed UVGI technology.

School officials were asked, “Since the start of the COVID-19 pandemic, which of the following steps to increase ventilation or filter/clean air supply to most schools (at least 50%) in your district.”

Mark-Carew and her colleagues said one of the limitations of their study was that school districts might have used means other the four choices that they were presented to improve air quality in their school buildings.

They noted that rural school districts were less likely to invested HVAC improvements and HEPA filters than districts in cities, suburbs or towns. The authors say that could be a matter of resources but also that opening windows of schools in in rural areas may mean less exposure to noise and air pollution than it would in schools in cities and suburbs.

They also found that school districts in the West were more likely to have reported replacing or upgrading HVAC systems than districts in the rest of the country. Mark-Carew and her colleagues say Western school districts may have newer buildings that are “more amenable to implementation of technological improvements compared with older buildingsin other regions.”