Let’s clear the air to prevent Covid-19 and the next pandemic


Abdulhaq Compier MD, The Netherlands

How Covid-19 spreads 

In May 2021, unfortunately, after debating the facts for more than a year, the World Health Organization finally acknowledged that Covid-19 is spread by “aerosols”. (www.nytimes.com/2021/05/07/opinion/coronavirus-airborne-transmission.html)

Aerosols are particles containing the virus that are emitted with the breath of an infected person and then float in the air, much like cigarette smoke. The more of these particles are inhaled by the people around, the more sick they become. In the outdoors, aerosols are easily blown away in the wind. But in unventilated spaces, they form dangerous clouds that can infect everyone in a room. Most infections have occurred when dozens of people were infected all at once, called “superspreading events”. Furthermore asymptomatic carriers, which means people who do not (yet) feel ill, can be the most infectious. This explains how large outbreaks could suddenly occur and nobody saw them coming. 

Create virus-resistant communities

Despite all these troublesome facts, this knowledge can also help us keep safe even while not having to lock ourselves up entirely. For example, it has been shown that only 0.1 per cent of infections occurred outdoors. (/www.irishtimes.com/news/ireland/irish-news/outdoor-transmission-accounts-for-0-1-of-state-s-covid-19-cases-1.4529036

Also, ventilation and air purification technology can greatly help reduce risks. If we work together, we can eradicate Covid-19 almost entirely from our communities even where vaccines are not yet available. The virus-resistant environment we thus create will, insha-Allah, also help prevent viruses like Covid-19 to take root in our communities in the future.

Avoid the Three Cs

In Japan, the main ways of transmission of Covid-19 were understood already in February 2020. Below, I will elaborate on their Three Cs strategy to help you reduce infection risks. I will also suggest technology to further increase your safety. Inform your boss at work, the principal at school and your social contacts about these recommendations to create your own protected social bubble. 

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Communication from the Japanese government, who adopted a wise strategy from the beginning of the pandemic.


Move social activities outside as much as possible. Only 0.1 per cent of infections occurs outdoors.

Cross-ventilate the room when you meet with other people. Open doors and windows on multiple sides of the room as wide as possible, but at least eight inches (20 cm). When ventilation cannot generate a tangible airflow, do not use the room.

Wear a face mask that fits well around the face. FFP2 or a well fittedwashable mask, preferably two layers of cotton and one of satin. Plastic face shields and screens do not offer protection. Children that cannot wear a face mask may benefit about an hour from Vicks applied under the nostrils. 

Shorten the duration of stay in spaces like shops to a maximum of 20 minutes (while also wearing a mask). 

Avoid narrow spaces like elevators and public toilets. You can get infected within minutes even after the infectious person already left.

In cars, wear a face mask,increase ventilation, open windows.

Do not use air-conditioning in an enclosed room. An aerosol cloud will build up because the air recirculates. The virus also survives longer in cold and dry air. Cross-ventilate the room or use HEPA air purifiers alongside the air conditioning. 


Limit the amount of people in a gathering to approximately 10 people especially when ventilation options are limited to one door and one window on opposite sides. This will reduce the odds of people in the gathering being infectious. It will also reduce the risk of prolonged close contact and will enable enough ventilation. Below is explained how CO2 metres can help keep larger gatherings safe. Gatherings outdoors are much less dangerous, but risks increase in wind-still conditions, with loud conversation, shouting or singing and with longer duration of close contact.


The 0.1 per cent of infections which happened outdoors were after a lengthy conversation (at least 15 minutes, but probably more like an hour) at close range, without a face mask. Wind-still conditions, loud conversation and singing increase the risk. Multiple shorter conversations on subsequent days can also cause infection. Indoors, keeping distance adds to your safety, but first make sure to ventilate well to prevent an aerosol cloud fills up the entire room. 

Most dangerous places to be in:Places where the Three Cs overlap. These are typically (karaoke) bars, church choirs, restaurants, classrooms, work and family meetings and gyms. Hotels, ships, care homes, prisons and apartment buildings are dangerous asventilation systems often move air from one room to another. Meatpacking factories have seen large outbreaks because of loud talking in recirculating cold air, in which the virus survives longer. Aeroplanes are generally safe with their top-down ventilation and HEPA filters, but the narrow toilets are dangerous.

A note on disinfecting objects: “Fomite” infection, through touching a contaminated surface and then touching the nose or mouth, has been assumed initially and is also still cautioned against in the communication from Japan shown above. However, it has been shown not to happen in real-life conditions (www.nature.com/articles/d41586-021-00251-4). Thus, disinfecting groceries seems like an unnecessary thing to do. Hand hygiene can be observed as usual.


Technology can help reduce infection risks significantly. At work, in schools and at home,make someone responsibleto study this technology, to select the products, to do maintenance and to instruct people about their use.

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CO2 meters 

In schools and other places where groups gather, CO2 meters ($ 60-250) can show whether enough fresh air is coming in to reduce the risk of superspreading. If the below maximum values are maintained by ventilating, plus all doors and windows are opened wide every two hours, the risk of an infectious person transmitting the virus is less than 5%. For maximum safety, a facemask can be used or air purifiers added. Prevent singing and shouting.

CO2 table Delta variant

HEPA air purifiers

H13 grade (“True”) HEPA air purifiers clean the air in homes, schools and offices using filters, ionization and/or UVC light. The CADR indicates the maximum clean air delivery rate of the device. But maximum settings are noisy, so choose a high CADR to ensure that also at lower settings, your devices clean the air in the room ideally five times per hour. Use one device per 25 m2 of floor surface.

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Affordable home devices can help reduce risks for single rooms. Larger buildings should review their HVAC systems to a create a virus-free indoor climate for the future.

Examples are the Blueair Classic 605 SM (high CADR); Winix Zero (affordable), HoMedics Total Clean 5 in 1 Tower Large (high CADR for a low price). The Philips AC3829/10 and Daikin MCK75 have a built-in air humidifier to keep humidity at 50%, which helps to kill the virus, but these require weekly maintenance. Prices start around $200. It helps to add a fan on the ceiling to prevent the accumulation of aerosols in one area of the room. However, avoid floor fans that blow air directly from one person to another.

The online version of this article was updated on 3 July 2021 to include guidelines on the new Delta variant and therefore differs from the printed version. These recommendations are per my understanding on 3 July 2021. They significantly reduce currently known risks including the Alpha and Delta variants (B117 ‘British’ and B1617 ‘Indian’ variant), but this may change for new mutations. For new research one can follow Nature magazine and authors Zeynep Tufekci, Linsey Marr and prof. José Luis Jiménez. For questions about this article, I can be emailed at h.s.compier@gmail.com.

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