The more deadlier a virus, the rest likely it is to spread. Let’s take ebola as an example which was very feared due to it being quite deadly, yet a flu-like virus managed to infect many orders of magnitude more people.

A counterexample: HIV is pretty deadly, but slow to progress, so it infected a lot of people. In countries with insufficient healthcare infrastructure (Subsaharan Africa), it actually killed a significant percentage of the population, precisely because it was so successful in spreading. Without modern medicine, it could have wiped out entire cultures, especially those that were more sex-positive.

(An interesting question to chew on is: what was the impact of religious sex taboos in pre-modern and early modern era? If monogamous couples were more likely to have healthy offspring and nurse their kids into adulthood, it might explain some of the societal swings towards puritanism in the 16th-19th century, which was a period of endemic syphilis.)

Indeed as you and another commenter pointed out correctly, it is not the whole picture, and given an intelligent, evil design one could possibly create a disease that spreads fast and kills only much later (by let’s say, causing cancer). But fortunately we are not inside Plague Inc.

But if I am not mistaken, from a strictly evolutionary perspective there is no pressure towards such a disease — a genetic variation that is more deadly won’t dominate over its less deadly variant and thus deadliness could be a variable that only changes randomly from the initial level (and decreasing if it is actively detrimental to spreading, where I would say that in case of a human population deadliness does correspond with fear).

But IANAE, nor a mathematician.

> The more deadlier a virus, the rest likely it is to spread.

Not really. The two primary factors controlling how fast a disease spreads is the infectiousness (R0 or other similar measures), and how long victims are infectious before they display symptoms.

The deadliness, the victim living or dying, happens significantly after they've finished their role as spreader of disease and thus does not significantly affect the spread.

Ebola fails to spread, not because it's deadly, but because the symptoms are almost immediate and dramatic.

(I took graduate level course in the mathematics of epidemiology and got an A, which makes me no expert at all, but this is fairly fundamental.)

I gave the OP another example of a deadly and yet widespread virus, HIV.

He is not completely off the ball, though. Our immune systems are rather good, so (with significant exceptions like HIV) if some virus doesn't kill us quickly, we tend to clear it out of the organism or at least get it under control, so it won't kill us at all.

Viruses that are very deadly but take a long time to kill you (thus enhancing the risk of transmission), like HIV, aren't very typical.

This is a weird argument to make. The rational thing is to make different decisions in different scenarios. The choices I would make for how/whether to participate in society, whether to take a vaccine, etc., would vary greatly depending on whether a given disease has a 1 in 50,000 chance of killing me vs if it's like something out of the movie Contagion that would have a 1 in 10 chance of killing me.

If covid had a 1 in 10 chance of killing me I would have made very different decisions over the course of the pandemic. You're saying that people would still behave the same as they did during covid no matter how deadly a given disease is, which seems pretty ridiculous.

My state took it just seriously enough to get us to vaccines (and even before that, buy some time until they realized they shouldn't just put everyone on a respirator). For all I know it may have saved my life and the life of several other people I know with comorbidities. Possibly my parents as well.

Yes, a third of the country didn't go through the effort and a lot of people died in those states also. The country might still be functioning, but not necessarily well, with significant labor shortages, supply chain issues, high inflation, a looming recession, record high gas prices, etc. (not all of that is directly because of the pandemic, granted, but it sure didn't help).

I think we're in violent agreement.