[feanaro]

> Reproducing more efficiently is a win for natural selection and will normally result in a dominant strain: whether that strain is more deadly or not is going to be random.

The conventional wisdom is such because a virus that is swiftly fatal and/or has more dramatic health consequences would have less chance to propagate to other hosts. For instance, because the original host will be unable to move or will look threatening to others so they will know not to reside close to them. This should make it less than random.

Unless of course some unforeseen factor makes this reasoning untrue.

[jfoster]

Taken to extremes, it's easy to see how a virus that is 50% fatal within 24 hours will not last long itself.

Is there really very much selection pressure between 1% and 2% fatality rates over 4 week timespans, though? Especially if immunity is conveyed by infection, I don't see any reason why a virus like that would evolve to be less fatal within the timescales that humans care about.

[JamesBarney]

Generally if it's twice as fatal it'll probably makes people twice as sick so they're more likely to go out less, stay home more, and less likely to infect other people.

However if it did damage in a way that doesn't manifest for a long time this wouldn't necessarily be the case. But that would be the exception more than the rule.