Let’s air the discussion about COVID

The communication to the population of the health measures to face the pandemic, have not placed enough emphasis on airborne contagion in interior spaces, one of the most common transmission routes and with the greatest impact in the increase in COVID-19 cases of according to science. Seminars have been organized and reports with scientific background on the subject have been published, but even in Chile we still have a lot of work to do to effectively communicate the measures that contribute to reducing the risk of contagion in this way.

When a person speaks, sings, shouts or exercises, it emits particles of a diameter similar to the fine particulate material that allows the virus to be transported. Outdoors it dissipates quickly and the sun finishes the job, efficiently disinfecting surfaces. Indoors it accumulates and the more people are gathered, the risk of contagion increases. Risk can be reduced by taking common-sense measures such as ventilating, opening windows, or reducing hyperemitting activities indoors, such as choir rehearsals, wind instruments, or exercise.

There are many scientists who try to communicate this transmission mechanism worldwide and have made estimates of the risks of contagion from institutions such as the University of Colorado or the Max Planck Institute. For example, it is estimated that a contagious person who speaks emits four times more viruses than a person who is silent. A person who speaks loudly or sings emits 30 times more. Whether a person is sitting, dancing, or exercising, it also affects how much they inhale and exhale. Wearing a mask can significantly reduce the emission. In the case of N95, in more than 90% of what is emitted or inhaled. A cloth mask captures much less, around 25 to 50%. Then it is possible to estimate different relative risks of contagion depending on what activities are carried out.

The virus concentration can then be estimated as a function of the sources (use of mask, or activity), size of the room, and if there is natural ventilation (windows and doors open), forced or if adequate filters of particles are used, in addition of the prevalence rate of the disease. In these estimates it can be determined that, in a typical classroom of a Chilean school with 30 students, the most effective measures are the use of a well-fitting N95 mask and ventilation (opening doors and windows), which combined with prudent distancing between students can reduce the relative risk of contagion by more than 90% versus closed windows and without the use of a mask. Wearing cloth masks nearly doubles this risk. The reduction in capacity reduces the amount of emission, but can be replaced with good ventilation and better use of masks.

Ensuring good ventilation by keeping windows and doors permanently open, promoting the proper use of quality masks and ensuring that there is a prudent distance between students are more applicable measures than strongly reducing capacity and having large groups of students connected remotely. Apart from the already known benefits of face-to-face education, remote education takes an immense effort in costs borne by parents, with the problems of inequity in digital connectivity, it can only be applied in a reduced portion of the territory. The best thing is to focus efforts on ventilation and the already known sanitary measures. Needless to say, singing and exercising indoors with other people presents a much higher risk.

In some schools in Santiago, measures such as ventilation and recommendation of N95 masks were applied. The estimated risk of contagion for these measures is 3% for a full month of classes vs. 47% without mask or ventilation. Upon entering quarantine, they had no outbreaks in rooms. Generally, the contagion occurred in social gatherings, with family, when the guard was lowered and the ventilation or mask was stopped.

This also applies to public transport. A bus or subway with open windows has much less risk of contagion than an airtight one, unless the particulate air is filtered at adequate rates. The correct use of good quality masks and keeping silent in these conditions also reduces the emission of particles, and this is practiced by different meters in other countries.

International studies have shown that in general the transport systems that maintain known sanitary measures and that also ventilate, have shown low rates of contagion. However, and in a context more similar to ours, the role of agglomerations in maintaining these levels of safety is still under discussion, even though there are optimal ventilation conditions. As long as the scientific evidence is not clarified, it is very important that in public transport, and as far as possible, an attempt is made to maintain the distance between passengers, since inhalation close to the source of the aerosols emitted by an infected person, even if there is good general ventilation and with an exposure similar to an average duration trip, could increase the risk of contagion. These apprehensions are explained because the viral concentration close to the person who emits the aerosol, could be high if the distance between people is very low (a scenario in which ventilation has not yet been able to dilute the viral load with fresh air) .

Let’s not ignore the most important route of contagion according to science. Let us give greater importance to ventilation and reduce efforts in other measures that have been confirmed as ineffective, such as the disinfection of bus stops or the street itself. Let’s stop believing that a screen is going to prevent a contagion of something that is transmitted through the air. That television channels use the N95 mask to set an example for the country, since the transparent face masks that some show on the screen only reduce the inhalation of potential infectious particles by 20%. Let’s help the population understand the importance of airborne transmission once and for all and put efforts into ventilation.

Let’s evaluate our measures by installing low-cost monitors that measure CO2 in closed spaces, to determine when the accumulation of our breath becomes risky. In the halls, in offices, on public transport and in our homes. We have years to fully return to normal. Putting aside airborne contagion indoors is only going to postpone that day coming. The country has many scientists and high-level professionals who are willing to contribute to generating practical measures to reduce the risk of contagion, let’s coordinate and act together to educate and create solutions that help our country.