When you have as few genuinely original ideas as I do, one way to make progress is to borrow (with appropriate attribution) other people’s ideas. I have been wondering about how a virus such as the corona virus (shown on the left as the knobbly object*) gets through the mucus (pale blue) that lines the inside of nose and throat, to attack the cells (pink) underneath this mucus. Viruses need to get inside our cells to take them over and allow the virus to reproduce.
One of the functions of mucus may be to trap or somehow to provide a barrier to the viruses. After some Googling it occurs to me that this problem of blocking movement of a virus is more-or-less the same as the problem water companies have, although the scales are very different.
Water companies are faced with dirty water, that may contain viruses. They need to filter out the viruses, to give us the the clean virus-free water we want in in our homes. Water companies either rely on natural filtration through rocks (as featured in ads for fancy bottled water, tap water also in many cases starts off filtering through rocks — another reason for giving bottled water a miss), and/or filter it themselves, through say a bed of sand. The porous rock/bed of sand should trap the viruses to protect our water. In an analogous way, the mucus lining the inside of our noses and throats should trap the virus to protect the cells beneath.
Water companies and engineers have done a fair bit of work on understanding how to trap viruses and protect water. We can learn from that work. In sand beds viruses stick to the surfaces of the sand and are trapped, on a much smaller scale mucus contains assemblies of sticky proteins that can trap viruses. Some of the ideas the engineers use to understand what makes a good water purification sand bed can be used to understand better when mucus protects us, and when it does not.
* The image was done with biorender, which I am playing around with and liking quite a lot. The image should have a biorender watermark but I had to crop the image.