The widespread use of high-quality masks, such as the N95 and PFF2, combined with monitoring of Covid-19 cases and other non-pharmacological measures, can keep the levels of transmission of the new coronavirus in schools very low, even in cities with low vaccination rate. In a scenario where no one wears masks, more transmissible variants such as the micron could infect up to 80% of the population. These are some of the conclusions of a study published on the arXiv platform in preprint version (not yet peer-reviewed).
The work is led by researchers from the Center for Mathematical Sciences Applied to Industry (CeMEAI), a Center for Research, Innovation and Diffusion (CEPID) of FAPESP based at the Institute of Mathematics and Computer Science of the University of São Paulo (ICMC-USP) , in San Carlos.
“High-quality masks, such as PFF2 and N95, are very effective in containing transmission and very cheap compared to the cost of ICU admission. [unidade de terapia intensiva]”, says Tiago Pereira, professor at ICMC-USP and coordinator of the study.
The work concluded that the use of poor quality masks (such as cloth ones) by students and education professionals would increase transmissions by five times compared to the scenario with closed schools. If students wear masks considered to be of good quality, such as surgical masks (50% filtering efficiency), and school staff use N95 or PFF2 masks (which have 95% filtering efficiency), the increase in transmission would be than three times, compared to the period without face-to-face classes.
The mathematical simulations that made it possible to reach the conclusions were based on epidemiological data from Covid-19, from health and education departments, a model of transmission in classrooms by aerosol and data on mobility of a population. In addition, information contained in the scientific literature on SARS-CoV-2 transmission was included.
The population that served as a model was Maragogi, on the coast of Alagoas. With 33,000 inhabitants, the city has income and demography representing about 40% of Brazilian municipalities. The researchers partnered with this and about one hundred other prefectures in order to collect data that could be used to guide public policies, as part of the research by the ModCovid19 Working Group.
The simulations were also calibrated for a large city, having Curitiba as a model. The results were similar.
air circulation
“We take into account, in the simulations, that people use the masks correctly and that the filtering is the one provided in the packaging by the manufacturers. The incorrect fitting of the mask on the face and other practices of the users can considerably reduce protection”, warns Pereira.
Therefore, the researcher adds that education professionals must be trained to guide students on the correct use of these personal protective equipment.
The study also shows that decreasing the number of students per class does not necessarily restrict the spread of the virus. Since the pathogen is transmitted by droplets of saliva, the low air circulation causes the particles to remain suspended for a long time, reaching even distant people in the classroom.
“The rooms have evolved for thermal comfort, they usually have air conditioning, so the air exchange is very low. This is disastrous for the transmission of Covid-19”, says the researcher. To give you an idea, in another study by the group, it was found that street markets did not offer a greater risk of transmission because they were outdoors.
Although non-pharmacological measures can be quite effective if well executed, even in closed environments, vaccination continues to be a factor in blocking transmissions, especially for teachers.
A study published in the journal Science has already shown that educators who teach face-to-face classes are up to 1.8 times more likely to become infected than those who work exclusively online. The fact that they usually speak loudly and move from one classroom to another makes them important vectors of transmission of SARS-CoV-2. Therefore, the vaccination of these professionals should be prioritized.
In addition to improving air circulation in rooms, the authors of the Brazilian study say that measures such as isolation of students and education professionals exposed to the virus, vaccination of risk groups and monitoring of cases contribute to the reduction of new infections.
The work has among its co-authors researchers from Alagoas, Rio de Janeiro and Mato Grosso do Sul, in addition to Italy, Germany and Cyprus. The research was supported by FAPESP through a doctoral scholarship granted to Edmilson Roque dos Santos.