[legionof7]

The reason that the Spanish Flu evolved into a more deadly strain was because WWI was going on. The mild cases stayed at the front lines while the severe ones went home and spread the severe strain around.

This won't happen here because the severe strain will die out. Viruses generally become less lethal as they spread.

[kyboren]

> This won't happen here because the severe strain will die out.

Can you please elaborate why this is the case? What if mild cases stay home while patients with severe cases go out looking for medical care, spreading it around? I know nothing about epidemiology, virology, etc. so I would appreciate a little hand-holding.

[_red]

Viruses are trying to replicate, not necessarily kill the host. Hence selection pressures will skew it towards “Antibody resistant, lower fatality”. The common-cold is the most successfully virus for a reason. It’s constantly being spread...which is all the virus ultimately “cares” about. (I know viruses / dna don’t have desires, I’m just using shorthand to discuss the selection pressures). Viruses that kill their host ultimately are losing a means of transmission.

[kyboren]

OK, I understand all this.

> Hence selection pressures will skew it towards “Antibody resistant, lower fatality”

But that's my question: Will it in this case? If those with severe symptoms are more likely to go out and spread the disease, wouldn't the more severe version be positively selected?

[ForHackernews]

People stay home when they feel like crap. I bet parent comment is right that severe symptoms are selected against.

[roenxi]

> Hence selection pressures will skew it towards “Antibody resistant, lower fatality”

That is pressure on the humans. All the humans that will die easily will die and all the survivors will be the more resistant ones.

The virus itself does not behave strategically. Species, other than humans, have no particular ability to plan how they evolve. The only pressures on the virus itself are for longer incubation times, faster ability to spread and the ability to reinfect people. Even if it could strategise there is no particular pressure on the virus whether it kills its host or not as long as it gets passed on to a few people in excess of the original host.

[Engineering-MD]

Not really true. The selective advantage is to viruses which can spread to more new hosts. The longer you keep the host arrive, the more new hosts are colonised. If it kills without spreading it’s not going to survive.

[flukus]

> Hence selection pressures will skew it towards “Antibody resistant, lower fatality”

Those selection pressures don't appear until the exponential growth slows down. From the virus perspective right now and in the near term it's super successful, so there's no need to adapt.

[pasquinelli]

Viruses undergo natural selection too. A virus that's less lethal has the host as a virus factory for longer. A virus with less overt symptoms is more readily spread to new hosts.

[totalZero]

The counterexample to this line of thinking is a lethal virus with a lengthy incubation period that can transmit while the host is asymptomatic.

[pasquinelli]

That's the history of syphilis if i understand correctly. It started out as a serious plague that covered its host in oozing sores and killed them in a couple months, now its symptoms are much less severe and it kills in a matter of decades.

[fxj]

You just described HIV.