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Something I have been wondering about, wouldn't a virus naturally evolve to be less deadly and more contagious over time? I.e. virus's tend to achieve a steady

Something I have been wondering about, wouldn't a virus naturally evolve to be less deadly and more contagious over time? I.e. virus's tend to achieve a steady state like the cold and flu in the long run. If you are too deadly it hinders spread so I would expect Covid to get less deadly and more contagious over time, which kind of fits the data?

kingbirdy 6y ago
Influenza isn't in a steady state, there are hundreds of strains[0] that compete with each other and recombine to form novel versions. Each year's flu vaccine targets four of them based on modeling as to which will be most prevalent in the upcoming flu season[1/2]. 0: https://www.cdc.gov/flu/about/viruses/types.htm https://www.cdc.gov/flu/about/viruses/types.htm 1: https://www.cdc.gov/flu/prevent/quadrivalent.htm https://www.cdc.gov/flu/prevent/quadrivalent.htm 2: https://www.fda.gov/vaccines-blood-biologics/lot-release/influenza-vaccine-2020-2021-season https://www.fda.gov/vaccines-blood-biologics/lot-release/inf...
vharuck 6y ago
Evolution is a random and long-term process. What you're thinking of is natural selection. Even that does not guarantee things will get better. For example, there was a worse second wave of Spanish Flu. Natural selection only implies there's less chance these terrible things will last. And, to adapt an economic adage, "The disease can remain deadly longer than you can remain alive."
- jacquesm 6y ago
  Natural selection is the basic mechanism that enables evolution, the one is part of the other.
hamaluik 6y ago
Generally, yes. But also we’re a bit unlucky that it isn’t very deadly: SARS was way deadlier To start with but as a result spread several orders of magnitude less (both naturally and because humans had a stronger reaction to “shut it down at all costs“). The H1N1 virus from the 1918 pandemic grew less deadly over time, and essentially evolved into a seasonal flu that is still affecting people around the world today. Personally, I expect COVID19 to go the same way.
- packetlost 6y ago
  The h1n1 is a bit of a strange case though because it jumps species boundary very often and mutates very quickly. COVID-19 appears to evolve much, much slower. Based on my limited understanding of virology, I think this means it's unlikely to become a seasonal problem unless the general populations immune system does not retain immunity to the same strain for a significant period of time.
  - djsumdog 6y ago
    We already know CoV2 rarely causes any symptoms in children. I wonder if there was a time in prehistory where common Rhinoviruses and Coronaviruses wiped out larger populations of elderly. Even if our immune system memory doesn't last very long for these types of viruses, wouldn't young people getting exposed to it now likely reduce its impact long term? It also seems like >95% of people who die from this are over 55 years old. When you get into your 70s~80s, aren't common colds one of the things that result in natural deaths, due to an aging immune system allowing pneumonia to set in where it wouldn't in a younger person?
    - johnchristopher 6y ago
      > We already know CoV2 rarely causes any symptoms in children. I wonder if there was a time in prehistory where common Rhinoviruses and Coronaviruses wiped out larger populations of elderly. Didn't pneumonia, influenza (among small pox and others) have terrible consequences on American native Indians ?
      - chrisco255 6y ago
        I believe small pox was the major one, I've heard among the Incas for example, it wiped out between 60 and 90 percent of the population. The main reason the colonists were able to spread so easily in the two continents is because disease wiped out huge swaths of the native population before many settlers even arrived. It's not like muskets are all that superior to bow and arrow (if at all, due to reload speed). Much of the land was just left vacant and unoccupied, and former cities abandoned.
2f3f23f32 6y ago
The COVID-19 mortality rates are dropping all the time and are at 0.2% now (barely higher than normal flu). I see no reason to prevent the virus from spreading now because it is not dangerous anymore.
- ReptileMan 6y ago
  This is the citation needed part of the discussion.
- reizorc 6y ago
  As far as I was aware it's the hospitalisation rate is driving the lockdowns more than the mortality rate.
  - adzm 6y ago
    Right, and as hospitals get overwhelmed, the mortality rate increases.
- remote_phone 6y ago
  0.2% mortality is the rate for people under 60. 0.1% rate for flu is considering all ages. If you remove over 60, the death rate for flu is something like 0.002%. So for an equivalent age group coronavirus is 100x more deadly.
- newsbinator 6y ago
  > it is not dangerous anymore How do you know?
- nocovidlockdown 6y ago
  https://edition.cnn.com/2020/10/28/europe/coronavirus-death-rate-second-wave-lower-intl/index.html https://edition.cnn.com/2020/10/28/europe/coronavirus-death-... By August, mortality rate is dropped to as low as 0.5% in the UK. -> Each day the virus becomes less deadly.
- nocovidlockdown 6y ago
  Yes, lets downvote the comment because it doesn't fit your personal opinion, even if it is confirmed by statistics.
onlyrealcuzzo 6y ago
Look for counter examples. Have we seen this in HIV? Smallpox? It's a plausibility. It's far from a guarantee. And the opposite, /could/ happen, too. The virus could mutate to have a longer incubation period, or be more deadly, or both.
- rimliu 6y ago
  I have seen a statemen somewhere tha for viruses it goes "transimissability, mortality, stealthiness: pick two". Not sure how true it is, but looks plausible.
  - Metacelsus 6y ago
    At least for natural viruses. Engineered ones could be extremely terrifying.
throwaway2245 6y ago
Conventional wisdom often claims that virus evolve to become less fatal - but I don't think that matches the historical record. There's evidence for influenza virus existing thousands of years before 1918. As such, it seems to have evolved into a much more deadly strain at that point. 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. We might optimistically anticipate some regression to the mean fatality rate (where the mean is close to 0).
- feanaro 6y ago
  > 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 6y ago
    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 6y ago
      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.
backtoyoujim 6y ago
I can imagine that a single nucleotide polymorphism doesn't care about what seems natural.
- neuronic 6y ago
  No, but its effect on the virus population kind of does.
  - backtoyoujim 6y ago
    Are you saying that a virus population has a conscience or morality ?
    - TheGallopedHigh 6y ago
      No the person is speaking about the evolutionary nature of the virus
sp332 6y ago
But the way viruses evolve to be less deadly is that the deadlier strains kill a bunch of people quickly, before they can spread too much. So that's not exactly reassuring for any given mutation.
scotty79 6y ago
Only if they are so deadly that it's harming their transmissibility.
davidf560 6y ago
I keep wondering what unintended consequences our nearly-unprecedented efforts on non-pharmaceutical interventions ("lockdown", social distancing, masks, etc.) might end up having on the virus - for example, could all our isolation and distancing be accidentally selecting for strains of the virus that transmit more readily over further distances?
- Zenst 6y ago
  That will be a tough one to measure. However measurement of the impact of lock-downs/social distancing upon existing known virus's like colds and flu's would give an insight into that whole area.
- estebank 6y ago
  The mitigations are effective in slowing the spread (to varying degrees, due to a multitude of factors), which in turn slow down the rate of mutation. In any case, I would expect the dispersion of the virus to follow a pattern similar to https://www.youtube.com/watch?v=plVk4NVIUh8 https://www.youtube.com/watch?v=plVk4NVIUh8
  - Fnoord 6y ago
    Don't know about your country/region but here the mitigations are put in effect because hospitals can't handle the pressure anymore.
Zenst 6y ago
That is mostly due to the way they are spread as a less impacted infected person would be more outgoing and spread that virus more. When somebody more impacted by a virus would be more isolated due to the impact. So the less impacting one gets more exposure and spread. So that in itself would be a factor, however virus can mutate in various ways and it is the mutations that effect the incubation period and that window of being infectious but not showing any symptoms - that is always going to impact things and certainly a large factor in why COVID managed to spread better than expected. But much hindsight and data analysis will play out for years and years, after all - we are still looking at the Spanish flu data and seeing different aspects to this day.
zerobits 6y ago
You would think – but viruses don't necessarily become less deadly. The virus wants to maximize transmissibility, and that might require trading off further against the host's health and increasing its death rate. An example is Myxoma virus. It was intentionally introduced to pest Australian rabbit populations (to cull them) and studied. After ~30 years of evolution, they found the dominant strain had a 70-95% death rate and left long-lasting lesions. Other strains with higher (~99%) and lower (~50%) death rates weren't as stable & prevalent. Once a virus is transmitted (enough), what happens to the health of its host is irrelevant. [1] https://www.sciencedirect.com/topics/immunology-and-microbiology/myxoma-virus https://www.sciencedirect.com/topics/immunology-and-microbio...
- libertine 6y ago
  It basically needs to be extremely contagious without symptoms that stop the spread - like killing the host. Which in part this virus has, asymptomatic and pre-symptomatic are as contagious as symptomatic. If it's enough to spread, doesn't matter much if the host dies after a few days or not.
  - tonyedgecombe 6y ago
    >Which in part this virus has, asymptomatic and pre-symptomatic are as contagious as symptomatic. Do we really know that yet?
    - libertine 6y ago
      >Infectiousness may peak before symptom onset (7). Viral loads appear to be similar between asymptomatic and symptomatic patients (8), although the implications for infectiousness are unclear. People experiencing symptoms may self-isolate or seek medical care, but those with no or mild symptoms may continue to circulate in the community. Because of this, those without severe symptoms have the potential to be “superspreaders” and may have an outsized influence on maintaining the epidemic. Source: https://science.sciencemag.org/content/370/6515/406 https://science.sciencemag.org/content/370/6515/406 While it's not confirmed they are more infectious, they walk among the community without being aware, therefore more prone for spreading.
nikolay 6y ago
It's not like the virus has a brain. Statistically most could become less deadly, but it doesn't mean all will follow the same pattern. In this case, the virus becomes less deadly as we know how to treat it better and most infected and tested now are younger people.
noodlenotes 6y ago
We're unlucky in that Covid takes such a long time to kill. It's a little under a week until symptoms onset, another week until serious illness [1]. Hospital patients aren't dying of Covid until almost 2 weeks after admission [2]. So we're talking about victims dying maybe a month after exposure. With other illnesses there's evolutionary pressure to be less deadly so that the host doesn't die before infecting others, but that's not a problem for Covid where people are most contagious before symptom onset. [1] https://www.cdc.gov/coronavirus/2019-ncov/hcp/clinical-guidance-management-patients.html https://www.cdc.gov/coronavirus/2019-ncov/hcp/clinical-guida... [2] https://www.bmj.com/content/369/bmj.m1923.full https://www.bmj.com/content/369/bmj.m1923.full
CyanLite2 6y ago
If you look at the death rate compared to March, it is dramatically lower, even though we're having 2x the cases. This could be because of better treatment, or because the virus itself is getting milder.
- Fnoord 6y ago
  Or because more people (with mild symptoms) get traced and tested. We had a shortage of tests and masks on start of pandemic.
- titzer 6y ago
  There are a lot of factors contributing, in particular the age distribution of those people getting infected. One thing is "viral load", which has to do with how much of the virus is present at initial infection. Because immune system response takes time to ramp up, e.g. 10x more virus in the beginning means that it can do much more damage before the immune response. It's likely that social distancing and masks have reduced the average viral load at infection time.
TheGallopedHigh 6y ago
In purely theoretical models virulence naturally evolved to a smaller value.

kingbirdy 6y ago

Influenza isn't in a steady state, there are hundreds of strains[0] that compete with each other and recombine to form novel versions. Each year's flu vaccine targets four of them based on modeling as to which will be most prevalent in the upcoming flu season[1/2]. 0: https://www.cdc.gov/flu/about/viruses/types.htm https://www.cdc.gov/flu/about/viruses/types.htm 1: https://www.cdc.gov/flu/prevent/quadrivalent.htm https://www.cdc.gov/flu/prevent/quadrivalent.htm 2: https://www.fda.gov/vaccines-blood-biologics/lot-release/influenza-vaccine-2020-2021-season https://www.fda.gov/vaccines-blood-biologics/lot-release/inf...

vharuck 6y ago

Evolution is a random and long-term process. What you're thinking of is natural selection. Even that does not guarantee things will get better. For example, there was a worse second wave of Spanish Flu. Natural selection only implies there's less chance these terrible things will last. And, to adapt an economic adage, "The disease can remain deadly longer than you can remain alive."

jacquesm 6y ago
Natural selection is the basic mechanism that enables evolution, the one is part of the other.

hamaluik 6y ago

Generally, yes. But also we’re a bit unlucky that it isn’t very deadly: SARS was way deadlier To start with but as a result spread several orders of magnitude less (both naturally and because humans had a stronger reaction to “shut it down at all costs“). The H1N1 virus from the 1918 pandemic grew less deadly over time, and essentially evolved into a seasonal flu that is still affecting people around the world today. Personally, I expect COVID19 to go the same way.

packetlost 6y ago
The h1n1 is a bit of a strange case though because it jumps species boundary very often and mutates very quickly. COVID-19 appears to evolve much, much slower. Based on my limited understanding of virology, I think this means it's unlikely to become a seasonal problem unless the general populations immune system does not retain immunity to the same strain for a significant period of time.
- djsumdog 6y ago
  We already know CoV2 rarely causes any symptoms in children. I wonder if there was a time in prehistory where common Rhinoviruses and Coronaviruses wiped out larger populations of elderly. Even if our immune system memory doesn't last very long for these types of viruses, wouldn't young people getting exposed to it now likely reduce its impact long term? It also seems like >95% of people who die from this are over 55 years old. When you get into your 70s~80s, aren't common colds one of the things that result in natural deaths, due to an aging immune system allowing pneumonia to set in where it wouldn't in a younger person?
  - johnchristopher 6y ago
    > We already know CoV2 rarely causes any symptoms in children. I wonder if there was a time in prehistory where common Rhinoviruses and Coronaviruses wiped out larger populations of elderly. Didn't pneumonia, influenza (among small pox and others) have terrible consequences on American native Indians ?
    - chrisco255 6y ago
      I believe small pox was the major one, I've heard among the Incas for example, it wiped out between 60 and 90 percent of the population. The main reason the colonists were able to spread so easily in the two continents is because disease wiped out huge swaths of the native population before many settlers even arrived. It's not like muskets are all that superior to bow and arrow (if at all, due to reload speed). Much of the land was just left vacant and unoccupied, and former cities abandoned.

2f3f23f32 6y ago

The COVID-19 mortality rates are dropping all the time and are at 0.2% now (barely higher than normal flu). I see no reason to prevent the virus from spreading now because it is not dangerous anymore.

ReptileMan 6y ago
This is the citation needed part of the discussion.
reizorc 6y ago
As far as I was aware it's the hospitalisation rate is driving the lockdowns more than the mortality rate.
- adzm 6y ago
  Right, and as hospitals get overwhelmed, the mortality rate increases.
remote_phone 6y ago
0.2% mortality is the rate for people under 60. 0.1% rate for flu is considering all ages. If you remove over 60, the death rate for flu is something like 0.002%. So for an equivalent age group coronavirus is 100x more deadly.
newsbinator 6y ago
> it is not dangerous anymore How do you know?
nocovidlockdown 6y ago
https://edition.cnn.com/2020/10/28/europe/coronavirus-death-rate-second-wave-lower-intl/index.html https://edition.cnn.com/2020/10/28/europe/coronavirus-death-... By August, mortality rate is dropped to as low as 0.5% in the UK. -> Each day the virus becomes less deadly.
nocovidlockdown 6y ago
Yes, lets downvote the comment because it doesn't fit your personal opinion, even if it is confirmed by statistics.

onlyrealcuzzo 6y ago

Look for counter examples. Have we seen this in HIV? Smallpox? It's a plausibility. It's far from a guarantee. And the opposite, /could/ happen, too. The virus could mutate to have a longer incubation period, or be more deadly, or both.

rimliu 6y ago
I have seen a statemen somewhere tha for viruses it goes "transimissability, mortality, stealthiness: pick two". Not sure how true it is, but looks plausible.
- Metacelsus 6y ago
  At least for natural viruses. Engineered ones could be extremely terrifying.

throwaway2245 6y ago

Conventional wisdom often claims that virus evolve to become less fatal - but I don't think that matches the historical record. There's evidence for influenza virus existing thousands of years before 1918. As such, it seems to have evolved into a much more deadly strain at that point. 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. We might optimistically anticipate some regression to the mean fatality rate (where the mean is close to 0).

feanaro 6y ago
> 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 6y ago
  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 6y ago
    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.

backtoyoujim 6y ago

I can imagine that a single nucleotide polymorphism doesn't care about what seems natural.

neuronic 6y ago
No, but its effect on the virus population kind of does.
- backtoyoujim 6y ago
  Are you saying that a virus population has a conscience or morality ?
  - TheGallopedHigh 6y ago
    No the person is speaking about the evolutionary nature of the virus

sp332 6y ago

But the way viruses evolve to be less deadly is that the deadlier strains kill a bunch of people quickly, before they can spread too much. So that's not exactly reassuring for any given mutation.

scotty79 6y ago

Only if they are so deadly that it's harming their transmissibility.

davidf560 6y ago

I keep wondering what unintended consequences our nearly-unprecedented efforts on non-pharmaceutical interventions ("lockdown", social distancing, masks, etc.) might end up having on the virus - for example, could all our isolation and distancing be accidentally selecting for strains of the virus that transmit more readily over further distances?

Zenst 6y ago
That will be a tough one to measure. However measurement of the impact of lock-downs/social distancing upon existing known virus's like colds and flu's would give an insight into that whole area.
estebank 6y ago
The mitigations are effective in slowing the spread (to varying degrees, due to a multitude of factors), which in turn slow down the rate of mutation. In any case, I would expect the dispersion of the virus to follow a pattern similar to https://www.youtube.com/watch?v=plVk4NVIUh8 https://www.youtube.com/watch?v=plVk4NVIUh8
- Fnoord 6y ago
  Don't know about your country/region but here the mitigations are put in effect because hospitals can't handle the pressure anymore.

Zenst 6y ago

That is mostly due to the way they are spread as a less impacted infected person would be more outgoing and spread that virus more. When somebody more impacted by a virus would be more isolated due to the impact. So the less impacting one gets more exposure and spread. So that in itself would be a factor, however virus can mutate in various ways and it is the mutations that effect the incubation period and that window of being infectious but not showing any symptoms - that is always going to impact things and certainly a large factor in why COVID managed to spread better than expected. But much hindsight and data analysis will play out for years and years, after all - we are still looking at the Spanish flu data and seeing different aspects to this day.

zerobits 6y ago

You would think – but viruses don't necessarily become less deadly. The virus wants to maximize transmissibility, and that might require trading off further against the host's health and increasing its death rate. An example is Myxoma virus. It was intentionally introduced to pest Australian rabbit populations (to cull them) and studied. After ~30 years of evolution, they found the dominant strain had a 70-95% death rate and left long-lasting lesions. Other strains with higher (~99%) and lower (~50%) death rates weren't as stable & prevalent. Once a virus is transmitted (enough), what happens to the health of its host is irrelevant. [1] https://www.sciencedirect.com/topics/immunology-and-microbiology/myxoma-virus https://www.sciencedirect.com/topics/immunology-and-microbio...

libertine 6y ago
It basically needs to be extremely contagious without symptoms that stop the spread - like killing the host. Which in part this virus has, asymptomatic and pre-symptomatic are as contagious as symptomatic. If it's enough to spread, doesn't matter much if the host dies after a few days or not.
- tonyedgecombe 6y ago
  >Which in part this virus has, asymptomatic and pre-symptomatic are as contagious as symptomatic. Do we really know that yet?
  - libertine 6y ago
    >Infectiousness may peak before symptom onset (7). Viral loads appear to be similar between asymptomatic and symptomatic patients (8), although the implications for infectiousness are unclear. People experiencing symptoms may self-isolate or seek medical care, but those with no or mild symptoms may continue to circulate in the community. Because of this, those without severe symptoms have the potential to be “superspreaders” and may have an outsized influence on maintaining the epidemic. Source: https://science.sciencemag.org/content/370/6515/406 https://science.sciencemag.org/content/370/6515/406 While it's not confirmed they are more infectious, they walk among the community without being aware, therefore more prone for spreading.

nikolay 6y ago

It's not like the virus has a brain. Statistically most could become less deadly, but it doesn't mean all will follow the same pattern. In this case, the virus becomes less deadly as we know how to treat it better and most infected and tested now are younger people.

noodlenotes 6y ago

We're unlucky in that Covid takes such a long time to kill. It's a little under a week until symptoms onset, another week until serious illness [1]. Hospital patients aren't dying of Covid until almost 2 weeks after admission [2]. So we're talking about victims dying maybe a month after exposure. With other illnesses there's evolutionary pressure to be less deadly so that the host doesn't die before infecting others, but that's not a problem for Covid where people are most contagious before symptom onset. [1] https://www.cdc.gov/coronavirus/2019-ncov/hcp/clinical-guidance-management-patients.html https://www.cdc.gov/coronavirus/2019-ncov/hcp/clinical-guida... [2] https://www.bmj.com/content/369/bmj.m1923.full https://www.bmj.com/content/369/bmj.m1923.full

CyanLite2 6y ago

If you look at the death rate compared to March, it is dramatically lower, even though we're having 2x the cases. This could be because of better treatment, or because the virus itself is getting milder.

Fnoord 6y ago
Or because more people (with mild symptoms) get traced and tested. We had a shortage of tests and masks on start of pandemic.
titzer 6y ago
There are a lot of factors contributing, in particular the age distribution of those people getting infected. One thing is "viral load", which has to do with how much of the virus is present at initial infection. Because immune system response takes time to ramp up, e.g. 10x more virus in the beginning means that it can do much more damage before the immune response. It's likely that social distancing and masks have reduced the average viral load at infection time.

TheGallopedHigh 6y ago

In purely theoretical models virulence naturally evolved to a smaller value.