Why hasn’t this been spotted by scientists? There have been literally thousands of papers researching epidemiological outbreaks. None seem to mention the concept of the human immune system reaching out to protect other people in a proactive way.
You’re seriously saying no one has even thought that part of immunity prevents an infected host infecting others?
Noooo, far from it. There’s a whole literature dedicated to what we might call transmission immunity… in insects. Here’s it’s called social immunity. What’s missing is an understanding this could be true for humans, as well as a precise definition of social immunity as a concept.
Likewise, there’s significant research carried out in psychology which looks at human behaviours associated with avoiding pathogens – behavioural immunity. But the idea that infected humans might actively prevent transmission as well as infection is missing.
Much of what we can consider transmission immunity is hidden in plain sight, by which many of the phenomena we associate with reducing infections would also reduce transmissions. This includes immunobiology, like the actions of T cells and antibodies, as well as the behaviours we associate with avoiding getting sick.
That the immune system works to prevent the host getting sick, instead of or as well as to prevent the sick host getting others sick, has never really been given much consideration in any of the literature, there’s just a strong inbuilt assumption implicit in every study that the immune system exists to protect the host.
In the early days of optics the assumption was that light was emitted from the eye, rather than towards the eye. Likewise there was received wisdom that planets and the sun orbited the earth. These philosophies “worked” in so far there was no cost in them being wrong, and explained the observed phenomena – that we could see, and that the planets and sun moved – fairly well.
For example, people appear to naturally socially distance themselves from strangers in choosing seats in restaurants, bars, cafe, buses and so forth. They naturally space themselves out, making it harder for diseases to spread. An epidemiologist would explain this as a means to reduce the risk of disease infection, but it would also have the effect of reducing the risk of asymptomatic disease transmission too.
Inbound and outbound disease are clearly different, but the avoidant behaviours can be identical, especially when you consider preventing infection for yourself would also prevent you from transmitting disease after you had become infected.
Why bother having it as a concept if infectious immunity is just transmission immunity?
It’s common to say, “All models are wrong, but some are useful.” Meaning that models are crude approximations of reality, but the simplifications enhance our understanding.
How you behave when you feel sick is very different to how you behave when you want to avoid people that look sick.
Transmission immunity is an essential concept in researching how evaporating mucus aerosols render containing pathogens noninfectious. Without this there’s no reason to investigate if this is even taking place, much less how it works. In eliminating airborne respiratory pathogens this is hugely important. It also explains why certain airborne diseases are different, for example smallpox and chickenpox, which can be transmitted through the skin in the spots they cause, can be understood as ways to evade the mucosal transmission immune responses. They imply that mucosal immunity is a significant obstacle in transmission as presumably the readily identifible marks would trigger strong avoidant behaviour in potential future hosts.
Another example is sickness behaviour, where almost all of the host behaviours can be explained as attempts to reduce the transmission risk… but that’s a subject for a different article.
[…] Why hasn’t transmission immunity been considered by immunologists, virologists, and epidemiolo… […]