Study reinforces importance of high-quality face coverings in schools

Mathematic simulations showed that well-executed non-pharmacological measures reduce the spread of COVID-19 even in places with low vaccination coverage. According to the authors, however, up to 80% of the population could catch the disease if preventive protocols are abandoned.

By André Julião  |  Agência FAPESP – Widespread use of high-quality face coverings such as N95 and PFF2 masks, in conjunction with monitoring of COVID-19 cases and other non-pharmacological measures, can keep levels of transmission of the disease in schools low, even in cities with low vaccination coverage. If no one wore a mask, more transmissible variants such as omicron could infect up to 80% of the population. These are some of the findings of a study conducted in Brazil and published without peer review on the preprint platform arXiv.

The study was led by researchers at the Center for Research in Mathematical Sciences Applied to Industry (CeMEAI), a Research, Innovation and Dissemination Center (RIDC) funded by FAPESP and hosted by the University of São Paulo’s Institute of Mathematics and Computer Sciences (ICMC-USP) in São Carlos, São Paulo state (Brazil).

“High-quality face coverings such as N95 and PFF2 masks are very effective at containing transmission, and very inexpensive compared to the cost of treating patients in ICUs [intensive care units],” said Tiago Pereira, a professor at ICMC-USP and principal investigator for the study.

The authors also state that when school students and staff wear cloth masks or other low-quality face coverings, the number of cases rises fivefold compared with the trend when schools are closed. When students wear surgical masks or other high-quality face coverings with 50% filtration efficiency, and school staff wear N95 or PFF2 masks with 95% filtration), the number of cases rises threefold.

The mathematical simulations that enabled the authors to arrive at their conclusions were based on COVID-19 epidemiological data, patient records, statistics from state and city departments of health and education, an aerosol classroom transmission model, and mobility data used to define population-wide isolation, as well as a review of the scientific literature on SARS-CoV-2 transmission.

The population of Maragogi, a town on the coast of Alagoas in the Northeast region of Brazil, served as a model. With 33,000 inhabitants, it is considered representative of at least 40% of Brazilian municipalities in terms of income and demographics. The researchers partnered with the Maragogi authorities and those of some 100 other municipalities to collect data that could be used to guide public health policies, as part of the research conducted by a scenario modeling group called ModCovid19. 

The simulations were also calibrated for a large city. In this case, the model was Curitiba, capital of Paraná state, with some 2 million inhabitants. The results were similar.

Poor ventilation

“In the simulations, we assumed that people wore masks correctly and that filtration efficiency was as stipulated on the wrapping by the manufacturer,” Pereira said. “Certain user practices can considerably reduce protection, especially not fitting the mask properly to the face.”

Teachers and other school staff should be trained to advise students on the correct use of face coverings and other personal protective equipment, he added.

The study also showed that having fewer students per classroom does not necessarily inhibit transmission of the virus, which spreads in droplets of saliva, and these can remain suspended in aerosol form for a long time in a poorly ventilated space, even reaching people some distance away across the room.

“Thermal comfort tends to be prioritized in classroom design. Most have air conditioning or heating, with very low rates of air renewal. That’s disastrous in terms of COVID-19 transmission,” he said. Another study by the group found that the risk of transmission was not especially high in street markets because they are open-air.

Although non-pharmacological measures can be highly effective even indoors, provided they are properly executed, vaccination is the best way to halt transmission, especially for teachers.

According to a study published in Science, teachers in the classroom are 1.8 times more likely to be infected than those who only work online. They tend to be major vectors of viral transmission simply by virtue of the fact that have to project in a loud voice and frequently move between rooms. Hence the importance of prioritizing teacher vaccination.

Air circulation in classrooms must be improved, the authors of the CeMEAI study argue. Measures such as isolation of students and teachers exposed to the virus, vaccination of high-risk groups and monitoring of cases also help combat transmission.

The co-authors of the article include researchers in other states of Brazil (Alagoas, Rio de Janeiro and Mato Grosso do Sul), and in Italy, Germany and Cyprus. The study was supported by FAPESP via a doctoral scholarship awarded to Edmilson Roque dos Santos. 

The article “Quantifying protocols for safe school activities” is available without peer review at: arxiv.org/abs/2204.07148.