of Cristina Marrone
Masks and spacing are not enough to avoid contagion via aerosols, especially with the more contagious Delta variant. Vaccines not yet available for children
Returning to school safely in September is a priority. World Health Organization, Unicef, governments and the principals of schools worldwide are pushing to organize themselves better with the aim of allowing students to return to the presence and forget the Dad that has created great disparities all over the world, with a collapse in the didactic preparation of students. But with infections on the rise, the Delta variant circulating, much more contagious, e most children not yet vaccinated, how will it be possible to return to the classroom avoiding new closures and quarantines? The solution exists and consists of a series of mitigation measures which, taken together, will change the cards and allow you to return to class safely.
Here they are: carbon dioxide detectors, ventilation, microphones for teachers, periodic screening of students and school staff with priority to those who have not yet been vaccinated. In addition they will be maintained masks e distancing, however, useful only to mitigate the spread of the virus in short distances due to the aerosol and to the droplets that fall to the ground due to the force of gravity typically within one and a half meters. But it is now clear that, especially the spacing, does not completely prevent airborne transmission in closed environments, where aerosol accumulates, saturating the rooms and can therefore be infected even at greater distances.
Microphones for teachers
So what to do? It is the Istituto Superiore di Sanità itself with the recent recommendations on sanitation that emphasizes two crucial aspects: reduce the emission of Sars-CoV-2 e promote ventilation. For Sars-CoV-2 it has been seen that when passing from simple breathing to speaking loudly or singing, the increase in the emitted aerosol particles increases up to 100 times. With the Delta variant, 60% more transmissible than Alpha, fewer particles are needed for contagion. For this reason in schools it is suggested to teachers, who must keep a high tone of voice to explain, to use microphones so you can lower your voice and emit less aerosols.
Carbon dioxide detectors
The ventilation aspect is more complex. Very few school buildings are equipped with mechanical ventilation which, on the basis of engineering data (room size, number of people present, activity carried out), can reduce the risk in the classroom with adequate air exchange. But almost all Italian schools have only simple ventilation available, i.e. opening doors and windows to exchange the air. When to do it? A big help can come from carbon dioxide detectors that constantly monitor air quality (measured in ppm, parts per million). Just recently Belgium has imposed them in public places so that the air quality and the level of safety are always visible, focusing on ventilation. More research has shown its effectiveness. Among the most complete is a recent study by a group of Italian and Australian experts who have been studying aerosol for years, followed by field work by the Italian Society of Environmental Medicine (SIMA).
Carbon dioxide sensors work a bit like a traffic light: green, yellow and red light based on the concentration of CO2 in the air with values set ad hoc for each environment. In this way, the teacher can intervene by opening the windows wide when the red lights go back to acceptable values. “However, the amount of CO2 cannot be correlated to the amount of virus emitted because speaking or breathing emits the same amount of carbon dioxide, while speaking, the increase in aerosol particles emitted by an infected subject increases up to 100 times “he explains Giorgio Buonanno, professor of Environmental Technical Physics at the University of Cassino, author of many works on aerial transmission. In any case, the CO2 detector system allows you to intervene quickly, safely, with set values defined in the most critical condition.
As already written several times in the winter season it is not so obvious to open the windows wide because it affects the thermal comfort of students and teachers, as well as energy waste. In the absence of mechanical ventilation, it is possible to use air purifiers with HEPA filters (High Efficienty Particulate Air filter) which replace natural ventilation (they cost about a thousand euros for a classroom).
Periodic screening in schools
The other weapon available to stop school outbreaks are periodic screenings of students and school staff as suggested by the European Center for Disease Prevention and Against (ECDC). “In September, swabs will be able to concentrate on environments where the vaccination rate is still low, such as schools,” suggests virologist Fabrizio Pregliasco. “With less invasive salivary tests, it will be easier to monitor even the smallest, who will be the last to be vaccinated.” A Canadian study recently published in PLOS Computational Biology conducted when there were still no vaccines concluded among other things that the best way to prevent outbreaks at school is to periodically test anyone who attends an educational institution. Instead, it seems that quarantining the entire class when a positive case is identified (what has been done in Italy and in many other countries) is a strategy that works little, because it is late. The researchers used a mathematical model to simulate how to prevent outbreaks. “We found that taking measures after a student has developed symptoms and tested positive is too slow a strategy. Screening of symptom-free students works quite well in our model and could also be applied in workplaces or shared housing, “he said. Paul Tupper, one of the authors of the study.
Vaccines naturally remain a winning strategy to limit the infection as much as possible. At this time, only those over 12 can benefit from the vaccine, but a large number of younger students remain uncovered. But when will even the little ones be vaccinated? Pfizer has announced that it will seek authorization for emergency use of its vaccine for children between the ages of 5 and 11 this fall. Moderna said the results of its clinical trial on young children are expected within the year and the American company applied for authorization to use its vaccine between the ages of 12 and 17 a month ago.
July 14, 2021 (change July 14, 2021 | 17:44)
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