Boosterism

[Speleofish]

Going back to pwhole's post, I'm not convinced that failing to vaccinate the world will have a serious, long term impact. Viruses evolve to infect as many animals as possible. Ideally, they do them very little harm so they can come back next year and do it all over again. Killing their new best friends is inefficient.

When they first encounter a new species, they're clumsy and tend to kill their new hosts (eg SARS, MERS, H5N1) but aren't very good at spreading. As they adapt, they attack different structures (eg airways rather than lung tissue), spread much more readily, cause less damage and give the organism time to fight back. I think this is where we are now with Omicron.

The implication is that further variants are likely to follow the Omicron route (more infectious, less deadly) rather than producing hideously lethal effects. Any new, dangerous variant will almost certainly be less infectious, so won't establish itself as a significant predatory virus. Consequently, from a purely European perspective, allowing the virus free rein across the rest of the world hastens the time when it becomes a fairly harmless common cold.

Clearly, there are uncomfortable ethical questions about using the rest of the world as a breeding ground. However, as Fjell points out, many developing countries with young populations, have greater health priorities and Covid isn't their biggest problem. Where it gets difficult is in partially developed countries like India which combine the problems of the developing world with a large, unhealthy middle class who are uniquely vulnerable.

Bottom line. I think Covid is likely to evolve into a nuisance rather than a disaster over the next year or two, though it may spring an occasional, unpleasant surprise. I'm aware that I have skipped over quite a few arguments - happy to expand if anyone wants. I only hope I'm right...

 

[pwhole]

I do worry about the uncomfortable ethical questions, but that's as much about them never leaving poverty than being at extra risk from covid. If they were better-off they could develop their own vaccines, surely? We will need to trade extensively with African countries if we want rare minerals for our essential electronic items, but if the plan is to just stomp in and take them, then we're possibly heading for Slavery V2.

In terms of our own population's general health and its approach to vaccines, I'm often reminded of this

https://www.youtube.com/watch?v=_-gJrmIL5BE

 

[al]

Viruses evolve to infect as many animals as possible. Ideally, they do them very little harm so they can come back next year and do it all over again. Killing their new best friends is inefficient.

When they first encounter a new species, they're clumsy and tend to kill their new hosts (eg SARS, MERS, H5N1) but aren't very good at spreading. As they adapt, they attack different structures (eg airways rather than lung tissue), spread much more readily, cause less damage and give the organism time to fight back. I think this is where we are now with Omicron.

Surely a virus isn't sufficiently sentient to warrant this level of anthropomorphism?

 

[Cantclimbtom]

...Bottom line. I think Covid is likely to evolve into a nuisance rather than a disaster over the next year or two, though it may spring an occasional, unpleasant surprise. I'm aware that I have skipped over quite a few arguments - happy to expand if anyone wants. I only hope I'm right...

That's certainly the hope and optimistically Omicron is the start of this. However the conjecture that this is necessarily how viruses progress is more assumption than science. I sincerely hope covid is going this way, but if you want some reading on this, I find McGill university have a lot of good resources
https://www.mcgill.ca/oss/article/covid-19/do-bad-viruses-always-become-good-guys-end
The point that this is largely a developed nation concern is also the same as a conversation I had with someone a few days back who is a hospital worker (radiographer) but he was saying he grew up in Zimbabwe so has a different perspective on infections diseases

 

[Speleofish]

In response to previous posts, I agree viruses aren't sentient and yes, you could say I'm guilty of inappropriate anthropomorphism. I should perhaps have said that if a virus evolves to become more infectious, it gains a survival advantage that allows it to outcompete the original virus. Viruses are more likely to achieve this if they develop the ability to bind to more accessible structures (eg the upper airway rather than the lung). Mutation is a random process but because successful mutations are rewarded, the end result looks very similar to intelligent design (hence my intellectually lazy anthropomorphism). This can can be a rapid process, as we have seen with Covid.

Over a longer period, viruses that cause relatively mild disease are rewarded as they can circulate continuously within the population. Some of this may be the result of viral mutation, some due to the development of immunity in the target population.

 

[Fjell]

If only all diseases mutated to be less virulent.

I once spent nearly a month in a West African hospital with undiagnosed typhoid being treated fruitlessly for malaria. I got the impression they only treated for malaria because that would be a very good guess there. In my more lucid moments I did reflect I had already had malaria and this seemed different. I had also taken Larium (which I suggest you don?t).

The streets were noticeably lined with churches. Fervent praying was about all many had going for them if you asked. The sort of place where drugs are sold per tablet, if at all.

I have very little patience with people in the UK who moan about how appalling things are here, but it?s just how it is. On a related point, I have forgiven Bill Gates for Windows.

 

[RobinGriffiths]

From my armchair... I can't see why a virus would become less virulent in order to come back next season. Surely the evolutionary selection event is when going from one host to another. There's no evolutionary pressure not to kill the host in order to come back for another go next year because that isn't the selection event. Assuming natural selection occurs at the individual rather than virus population level.

 

[Speleofish]

I think the most likely reasons for a reduction in virulence for respiratory viruses (apart from host immunity) are first, as viruses become more infectious, so the dose needed to cause disease is lessened, thus the initial disease burden is reduced. Second, by binding to receptors in the nose and throat, they don't initially affect critical organs. They may still spread to include the lung but there is an inbuilt delay which may allow the host more time to develop an immune response so that the severity of the subsequent pneumonia is reduced.

 

[HardenClimber3]

I think that in general terms it isn't a given that viruses evolve to become milder, though viruses that persist may cause less disease. It might be comforting to us to think that is so.... It is also important to remember that for most infections causation of disease is just an unfortunate accident. The severity of disease doesn't confer any particular advantage in most situations (okay, norovirus, anthrax, ebola are perhaps obviousexceptions).
Can you explain why a smaller minimum infective dose results in milder disease for any particular infective dose? Everything else being equal (big ask) there may be more milder cases, but the most severe cases would be similar (or worse). The mean severity of illness might be less (depending on so many other factors), but the absolute number of cases with severe disease will be similar (or greater). It then gets complicated if other factors enter...site of infection, local rates of multiplication, amount of virus shed and how it is spread).
Infection is often a race between host immune response and viral multiplication as you suggest, once basic barriers of infection have been over come.

 

[Speleofish]

With regard to disease severity, viruses that cause severe disease tend to incapacitate their hosts so they cant't spread it to others so easily. Mild infections allow the host to continue to interact with more people, so increasing the pool of people vulnerable to infection, thus giving a survival advantage to the virus. I think Omicron is probably an example of this but I accept that the apparent reduction in severity may represent the effect of increasing population immunity due to previous infections and vaccination. However, if you look at the Zoe data, at least 50% of people with Omicron have symptoms indistinguishable from the common cold. This is very different from wild-type or alpha infection which caused a more obvious lower respiratory infection, Delta being intermediate in this regard. Ironically, the best evidence for this being true or false is likely to come from China where their homegrown vaccines have very little efficacy against Omicron.

The minimum infective dose, defined as the lowest number of viral particles that will cause infection in 50% of people infected, correlates with severity of disease for a number of viruses, including influenza, measles, HIV and some coronaviruses (Van Damme et al; Med Hypotheses 2021 Jan; 146: 110431). In part this may be due to our non-specific innate immune response to viruses, mediated by interferons and cytokines which acts rapidly to eliminate small numbers of viruses and buys time for our specific immune response to take effect, which takes two-three weeks. This remains hypothetical for Covid at present as there are numerous other factors that contribute to disease severity (age, hypertension, diabetes etc). The idea of modifying the infective dose is also part of the suggested mechanism for some of the nasal sprays which are being developed to reduce Covid transmission, and which show some promise.

With regard to your last point, I agree that an increase in infectivity with only a modest reduction in disease severity will produce many more cases of disease. Some of these will be severe and the net effect may be to increase the total number of people requiring hospital treatment even if the risk to an individual is reduced. Whether or not this is the case with Omicron isn't yet clear. However, Omicron could be regarded as only one step towards the final, fully evolved Covid virus. Thus far the steps we have seen (wild-type, alpha, delta, omicron) have all shown an increase in transmissibility but with no significant reduction in severity. Delta started to show a preference for infecting the airways and upper respiratory tract rather than the lung, but the change was insufficient to cause a large difference in severity. Omicron has taken this further and one can hope that future mutations will produce viral clades that are less dangerous still. For a new, more pathogenic clade to take hold, it must either be more transmissible than Omicron or it must evolve when the current pandemic has receded so that there is little Omicron around so it has little virus to compete with.

Overall, I remain optimistic. However, I accept there are a number of hypothetical arguments here and events may prove me very wrong.

 

[Speleofish]

Just to clarify, I should have said there is a correlation between the initial dose of infection for influenza, measles, HIV and some coronaviruses, not 'the minimum infective dose'

 

[braveduck]

Looking at the severity of the infection in different groups ,I think
the income from cigarette tax will be much lower when this pandemic is over !