Maintaining masking requirements at Boston Public Schools protected students, staff
Districts that lifted masking requirements saw significant increases in COVID-19 cases among students and staff, compared to Boston
Peer-Reviewed PublicationHARVARD T.H. CHAN SCHOOL OF PUBLIC HEALTH
Boston, MA – The lifting of masking requirements in school districts outside of Boston in February 2022 was associated with an additional 44.9 COVID-19 cases per 1,000 students and staff in the 15 weeks after the statewide masking policy was rescinded. This represented nearly 12,000 total COVID-19 cases or 30% of all cases in those school districts that unmasked during that time, according to a new study led by Harvard T.H. Chan School of Public Health, the Boston Public Health Commission, and Boston University School of Public Health.
“Our study shows that universal masking is an important strategy to reduce transmission in schools and one that should be considered in mitigation planning to keep students and staff healthier and minimize loss of in-person school days,” said [CT1] [DT2] Tori Cowger, corresponding author and Health and Human Rights fellow in the FXB Center for Health and Human Rights at Harvard Chan School. “Our results also suggest that universal masking may be an important tool for mitigating structural inequities that have led to unequal conditions in schools and differential risk of severe COVID-19, educational disruptions, and health and economic effects of secondary transmission to household members.”
The study was published online in the New England Journal of Medicine, Nov. 9, 2022.
When Massachusetts rescinded its statewide universal masking policy earlier this year, many schools in the state, including those in the greater Boston area, lifted their requirements over the next several weeks. However, two school districts—Boston and Chelsea—maintained universal masking policies through June. That staggered lifting of masking requirements gave the researchers the unique opportunity to examine the impact of lifting those requirements on the incidence of COVID-19 among students and staff across 72 school districts in the greater Boston area.
The researchers found that before the statewide masking requirements were lifted, the trends in the incidence of COVID-19 observed in the Boston and Chelsea school districts were similar to the trends in the districts that later lifted masking requirements. After the statewide policy was rescinded, the trends diverged, with a substantially higher incidence observed in districts that lifted masking requirements compared to districts that maintained their masking requirements.
The findings also showed that the effect of school masking policies was greatest during periods when COVID-19 incidence was highest in surrounding cities and towns, suggesting that implementing universal masking policies during times of high transmission would be most effective.
“This study provides clear support for the importance of universal masking to reduce transmission of COVID-19 in school settings, especially when community COVID levels are high,” said study co-author Eleanor Murray, assistant professor of epidemiology at Boston University School of Public Health. “Masking reduces COVID-19 transmission in schools in an equitable and easy to implement way and should be part of any layered mitigation strategy.”
“Lifting Universal Masking in Schools—Covid-19 Incidence among Students and Staff,” Tori J. Cowger, Eleanor J. Murray, Jaylen Clarke, Mary T. Bassett, Bisola O. Ojikutu, Sarimer M. Sánchez, Natalia Linos, Kathryn T. Hall, NEJM, online Nov. 9, 2022, doi: 10.1056/NEJMoa2211029
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About Boston University School of Public Health
Founded in 1976, Boston University School of Public Health is one of the top five ranked private schools of public health in the world. It offers master's- and doctoral-level education in public health. The faculty in six departments conduct policy-changing public health research around the world, with the mission of improving the health of populations—especially the disadvantaged, underserved, and vulnerable—locally and globally.
JOURNAL
New England Journal of Medicine
METHOD OF RESEARCH
Observational study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Lifting universal masking in schools—Covid-19 incidence among students and staff
ARTICLE PUBLICATION DATE
9-Nov-2022
A new air purification strategy might reduce the risk of COVID-19 transmission in classrooms and other indoor spaces by as much as tenfold
University classrooms are forums for intellectual exchange. But the COVID-19 pandemic has highlighted how important it is for classrooms to also be sites of efficient air exchange—that is, good ventilation.
Air sampling technology developed by Constantinos Sioutas, a professor at the USC Viterbi School of Engineering, helped pave the way for the understanding that COVID-19 is an airborne virus. When the virus is exhaled in small respiratory droplets in indoor environments, the water content quickly evaporates because of the much lower relative humidity indoors than outdoors, leaving viral particles suspended in the air. That insight, in turn, led to the knowledge that replacing indoor air with fresh or filtered outdoor air (aka “air exchange”) can help dissipate viral particles that would otherwise linger for hours.
Now, a new study by Sioutas and his team conducted in USC classrooms demonstrates that high-efficiency in-line filters within HVAC systems can significantly improve indoor air quality. The study, published in the International Journal of Environmental Research and Public Health, also reveals that operating such a system at the same time as a portable air purifier with a HEPA filter can maximize the removal of tiny airborne particles.
Running these filtration systems simultaneously, “You reduce the risk of the students and the professor becoming infected [with COVID-19] by more than tenfold,” says Sioutas, Fred Champion Professor and Professor of Civil and Environmental Engineering and Aerospace and Mechanical Engineering.
The study’s implications extend well beyond USC to other educational institutions, as well as to residences, businesses and public transportation.
When Sioutas’ team began planning the research in the summer of 2021, they used data from USC Facilities Planning and Management (FPM) to determine which classrooms to evaluate. They wanted to measure indoor air quality across a range of building ages, classroom sizes and ventilation systems.
For the study, Sioutas’ team selected nine classrooms in seven different buildings, all of which had HVAC systems with MERV-14 in-line filters—except for one, which had a MERV-13 filter. MERV stands for the Minimum Efficiency Reporting Value; the higher the MERV rating, the more efficient the filter is in capturing particles from the air.
Eye-popping results
Sioutas was interested in measuring the effect of ventilation and filtration not only on pollutants we exhale, including carbon dioxide (CO2), but also on particulate matter (PM) that can infiltrate indoors and negatively impact human health. Indoor air pollution causes almost 3.8 million premature deaths annually, according to the World Health Organization (WHO).
His team first evaluated air quality in the nine classrooms during two-hour lectures, while students were present and the ventilation systems were operating. It turned out that all of the ventilation systems had high enough air exchange rates to dilute indoor CO2 concentrations to safe levels recommended by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). But when it came to reducing PM and particulate number (PN) concentrations, ventilation systems with MERV-14 filters were far superior to the one with the MERV-13 filter. The former reduced PM and PN concentrations by more than 80 percent, while the latter reduced them to 49 percent and 55 percent, respectively.
Next, Sioutas’ team repeated the air quality measurements while concurrently operating a portable air purifier. When Sioutas saw the first results, he was incredulous. Within 15 minutes, PM and PN were reduced to less than 10 percent of their initial values. In some classrooms, he says, the aerosol concentrations approached those of a semiconductor-industry cleanroom, which is a factory where PM is stringently controlled to facilitate the manufacture of silicon wafers into semiconductor chips.
Sioutas figured there must have been some mistake in the calculations. “I told my students, ‘Go back and do this experiment again—these results cannot be right,’” he says. But the results held. “That’s when we realized that once you activate the purifier…you have this drastic reduction in the pollution.”
In the second part of the study, Sioutas and his team introduced an indoor source of air pollution—nebulized sodium chloride particles, which were roughly the same size as exhaled COVID-19 particles—to an empty classroom. Operating the ventilation system along with the air purifier at its highest speed reduced the concentration of sodium chloride in the air to less than 10 percent of its initial value in about 15 minutes. Since the risk of airborne virus transmission is directly proportional to an indoor space’s viral aerosol concentration, the results suggest a more than tenfold reduction in COVID-19 risk.
Air purifiers with HEPA filters work by forcing air through fine mesh made of plastic or fiberglass fibers that capture tiny particles. Since COVID-19 cannot survive on most solid surfaces for long periods, the viral particles trapped on the filter die off, posing no further risk.
Sioutas hopes that the study draws renewed attention to the importance of air purification in COVID-19 prevention in educational institutions. He notes that portable air purifiers are an effective, affordable and energy-efficient way to slash the risk of COVID-19 transmission not just in classrooms, but in any indoor environment: “homes, restaurants, pubs, movie theaters, office buildings, sports arenas, you name it,” he says.
“I’m a fierce advocate of using this technology,” he adds. “I could not recommend it more strongly.”
JOURNAL
International Journal of Environmental Research and Public Health
METHOD OF RESEARCH
Experimental study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
The Role of Portable Air Purifiers and Effective Ventilation in Improving Indoor Air Quality in University Classrooms
ARTICLE PUBLICATION DATE
7-Nov-2022
