Disclaimer: the material presented on this page is my creative opinion formed from non-canonical sources about COVID-19 (I “connected the dots” if you will, but you can check the references yourself). This is not official advice. The canonical source should be guidelines from WHO or CDC.

I would try to follow the official guidelines if their recommendations are accessible to the general public. The general guidance is to wear masks, disinfect, and get vaccinated. However, in the early days up to a year into the pandemic, it was still hard to find disinfectants and N-95 masks. The situation improved as vaccines became generally available to everyone.

But in the mean time, I had to get a little creative. This may still be helpful in case a new strain emerges that is resistant to the vaccine.

Officially, EPA List N is the approved list of disinfectants effective for killing COVID-19. It lists products that consist of only Citric Acid. According to prior research, other human coronaviruses are found to be deactivated in acid < pH 4 and in base > pH 8. It works because the envelope of coronavirus, which is responsible for the infection mechanism, is a protein that could be denatured.

Lemon juice and vinegar have pH around 2-3, so they are suitable for disinfecting. Since pH 3 is 10x as diluted as pH 2 (pH is in negative log10 scale), they can be effective even after diluted 1:1 with same part water. Also, in some municipalities, drinking water is treated with alkaline to pH 9 in order to prevent pipe corrosion. This also prevents COVID-19 from spreading through drinking water in those municipalities.

Personally, I make disinfectant from food grade citric acid. To make a 2.5% solution which has pH ~2.4, use 25 grams of crystal citric acid in 1 liter of water. A one pound bag of citric acid crystals lasted me 9 months. It takes very little storage and leaves no odor. It is also edible so you can use it to disinfect groceries without worrying about residues. I find that food disinfected like this lasts a few more days longer, so I might continue to do this even after the pandemic.

Soap and water is also effective disinfecting. It works because the membrane of the coronavirus is held together by surface tension, which is disrupted by soapy water and other surfactants (the same article also explains that the lung needs surfactant to help with the oxygen exchange, and coronavirus kills the cells that produces the surfactant which results in difficulty breathing). Isopropanol and ethanol alcohols also work as effective disinfectants by reducing surface tension (you can literally see this in the form of wine tears).

However, disinfectants are probably not as relevant anymore because COVID-19 is now understood to be spread mostly airborne. WHO now recognizes the importance of building ventilation and air filtration. CDC additionally recommends ultraviolet germicidal irradiation (UVGI) as a supplement. There is a sentiment that scientists have discredited the Miasma theory—that diseases come from “bad air”—so thoroughly that it had forgotten how to prevent airborne diseases.

The reason why fresh air is effective in preventing airborne disease is because of the Sun, which emits powerful visible light and the invisible UV light spectrums UVA, UVB, and UVC. UVC is the most effective for germicidal purpose but is mostly filtered out by the ozone layer. However, even UVA and UVB can indirectly damage the DNA when the damage is extensive. UV light also causes RNA damage.

I suspect this is why in Taiwan and other South East Asian countries, COVID-19 spread is mostly curtailed. In addition to the prevalence of mask wearing there, most households have bug zapping lamps which use UV light to attract insects. We can’t see UV, but UV lamps also emit some visible wavelength as a byproduct. When choosing a UV lamp product, avoid UVA which is the least effective; it looks like the “black light” party light that has a purple hue. UVB, which is mildly effective, appears pale blue. UVB can slowly irradiate its surrounding without airflow. UVC lamp is typically enclosed for safety reason, so air purifiers have to induce an airflow through it in order to work. This may render it counter-productive as the air has to travel and potentially spread the pathogen before it can be disinfected.

In a public space where people gather, deploying bug zapper lamps might actually be an effective deterrent to the spread of COVID-19.