Sherlock Holmes in “Silver Blaze” solved the mystery of the murder of a racehorse’s trainer by observing that the dog did not bark when the horse was removed from the stable at night.
With COVID-19, are you as curious as I am about why the fraction of infected patients who are asymptomatic is so high? (Someone once told me that I am more curious about everything than he is about anything, so maybe you aren’t). But I always find it interesting when something seems out of sync.
There are multiple reasons that could explain this.
DIFFERENCES IN THE ACE2 RECEPTOR PROTEIN.
It might be because there are slight variations in the ACE2 receptor, either in the protein’s amino acid sequence, the pattern of glycosylation or the HLA patterns and genetics of the individuals. These variations might result in a lower actual viral load getting into cells, a slower infection rate and a better chance for the immune system to react prior to severe disease being exhibited.
PREEXISING PARTIAL IMMUNITY.
It might be because there is some preexisting immunity in the population. This phenomenon is reasonably common. We have heard a lot about the 1918-19 Spanish Flu pandemic. One of the strange elements of this terrible disease was that most of the lethality occurred among healthy young adults, not among the elderly or the compromised population. This is certainly counter-intuitive. To appreciate why, you need to understand a little bit about the influenza virus. It has two main proteins on its surface, “H” and “N”, hence the designation H1N1. The subscript describes variations of each of the proteins in different strains. The H protein is responsible for binding to the cell surface, the N protein is responsible for helping the virus enter the cell. (In coronavirus, both functions are performed by the Spike protein). Immunity against the H protein will prevent infection, while immunity against the N protein, although not protective, will reduce the severity of the disease.
With respect to the Spanish Flu, it is thought that there had been a previous strain of influenza that had circulated as much as 30 years prior, in which the virus had the same N protein but a different H protein. So, when the pandemic hit, those elderly patients already had some immunity against the N protein, and therefore, had a reduced severity of disease, while the younger people, with no such preexisting immunity, suffered huge amounts of death.
The same may be true in the current population. Perhaps immunity to one of the other proteins on the COVID-19 surface (and there are between 3 and 4 other proteins) can reduce the lethality of infection, and people who had seen other coronaviruses with these proteins are already immune. Those people would not have been identified as yet because, first, we are not doing antibody testing of the general population; second, because we are only looking for antibodies against this specific virus, and most often against the Spike protein; and third, because we are not correlating antibody presence with virus presence, so if we see antibodies we don’t know if they existed prior to an infection.
VIRTUAL VACCINE
This is total speculation on my part. I have seen no evidence or studies on this.
That said, here is my thinking.
This is not a very robust virus. It falls apart pretty easily when exposed to heat, UV light, detergents, alcohol and drying. What happens when it falls apart? What does virus “death” look like? It is not that the virus suddenly disappears like the wicked witch when doused with water. It is not that is disappears in a cloud of ash like the Nazi soldier in the “Raiders of the Lost Ark”. No, it is far more mundane. Constituents are broken apart and separated, more like hitting a pocket watch with a sledgehammer. Neither the pocket watch nor the virus remains functional. The watch can no longer tell time, and the virus cannot cause infection.
But the important thing here is that the pieces of the watch and the proteins of the virus still remain although they may be intact or partially destroyed. So, consider a situation in which there is virus on a surface. Light, heat or drying causes the virus to be “killed”. The result is that the surface no longer contains virus particles that are contagious, but there may still be viral protein sitting on it. Now, consider you touch that surface and then your mouth or nose. You would be placing those proteins into your body. There is no, and I want to be perfectly clear here, there is NO chance that you will get any disease from those proteins. Without the lipid envelope of the virus to organize the proteins, and without the RNA from the inside, there can be no disease.
Actually, what you have just done is vaccinate yourself. One of the most common forms of vaccines use the proteins of a virus, suspended in solution to generate an immune response.
So, it may be that in certain environments, very small amounts of destroyed COVID-19 virus are being given daily to people circulating through those environments, effectively giving them “virtual vaccines”, with multiple doses, allowing them to develop a preexisting protective immunity.