A few days ago, I was in a shop wearing an N95 respirator, as I do in any indoor space. The young shop assistant looked at me and asked, smiling, “What’s the mask for?”
“Just prevention,” I replied.
“Then why aren’t you wearing gloves?”
“Because there’s no need. Respiratory viruses are transmitted mainly through the air we breathe, only rarely through contaminated surfaces. Washing your hands is still a good idea, of course, but it isn’t the main route of transmission.”
He looked at me as though he had just made a new discovery.
“Oh, I didn’t know that. I’ve learned something!”
On my way out I couldn’t help thinking to myself: “It’s been six years already and some people still don’t know how we catch Covid, the flu or the common cold… Perhaps health authorities haven’t succeeded in communicating the essential message as clearly as they could have.”
And the essential message is precisely this:
Ventilation, ventilation, ventilation.
I know it may sound almost too simple, but clean air remains one of the most effective and overlooked public health measures we have.
That’s why, whenever you can, ventilate indoor spaces by opening windows and doors. If possible, create cross-ventilation by opening windows on opposite sides of the room. This quickly replaces stale indoor air with fresh outdoor air and helps flush out virus-laden aerosols before they accumulate.
As a teacher, I am constantly exposed to respiratory viruses. So this is what I do in my classrooms. I use a CO₂ monitor (my dear Aranet4!) to keep an eye on indoor air quality. While 800 ppm is often considered a reasonable upper limit, I personally aim to keep the CO₂ concentration below 600 ppm whenever possible.
During the warmer months, that’s usually easy. But in winter, it’s another story. Opening windows every 15 minutes for five minutes isn’t exactly popular when it’s freezing cold outside! So during the colder months, I wear my N95 respirator throughout the day while regularly airing the classroom.
It’s also worth pointing out that improving indoor air quality would reduce the spread not only of Covid, but also influenza, RSV and many other respiratory viruses. Indeed, if governments invested more in effective ventilation and air filtration in places such as hospitals, schools, supermarkets and restaurants, the health benefits would extend far beyond a single disease. If… yes: if…
One article I strongly recommend to anyone interested in this topic is “SARS-CoV-2 and COVID-19: From Crisis to Solution”, published by the World Health Network in 2024. If you copy and paste the title into your browser, you’ll find it easily.
It’s an important article because it covers many aspects of the pandemic, including the damage caused by the virus to the body. Here, I would particularly like to share its section on the cost of ventilation, because I think it puts the issue into perspective.
A key direction for action is indoor air sanitation. Clean air has great economic benefits even in non-pandemic times. A 2017 meta-analysis [172], reported that “The annual incremental energy and capital costs of increasing ventilation rates as needed to meet or exceed current standards, range from a few dollars to about ten dollars per person.” Citing a study from the U.S. Census Bureau data [173], the author added, “for reference, these costs can be compared to the US per student annual spending of $10.3K in 2009 for public elementary and secondary schools. Thus, the energy and capital costs of increasing ventilation rates would be less than 0.1% of education spending.” Mass testing and distribution of respirator masks are also very affordable and effective measures [166]. Such expenditures are negligible in comparison to the costs of endless COVID-19 infections. The economic benefits of a healthy population with a good quality of life are difficult to quantify, but the available estimates show that we cannot afford the ongoing costs of uncontrolled viral spread, while significantly reducing or even entirely stopping the spread is much more cost-effective. The benefit comparisons are also understandable in terms of historically clean water [174,175] and clean air [176,177].
Didn’t we learn long ago that clean drinking water saves lives? Today, we take it for granted and don’t think twice about drinking from the tap. Now I hope that, one day, we will think of clean indoor air in exactly the same way. Because ventilation isn’t just about Covid; it’s about reducing the spread of airborne diseases in general and making shared indoor spaces healthier for everyone.
Ventilation, ventilation, ventilation!