Why is Omicron apparently less virulent?

[mistermack]

It seems to be confirmed now, that Omicron causes a less severe set of symptoms, on average. Any suggestions as to why, when it is clearly far more efficient at infecting a host? 

My suggestions are 1) That the raised infectiousness somehow causes a quicker and bigger response from the immune system, resulting in a less severe illness. That might be bad news for people with a weakened immune system. 

2) Maybe the raised infectiousness means that more vaccinated people are catching it, and that they are getting less ill, and therefore affecting the figures. You could check that out, by looking at the figures for the percentage of vaccinated people who are testing positive, and how it compares to pre-omicron times. 

3) Because it's so much more infectious, it might be succeeding in infecting more young people than previous variants, resulting in less serious symptoms on average. 

I would like to see an analysis of how people of my age (71) fare on average, when they catch it, and compare that to Delta etc. 

[exchemist]

18 minutes ago, mistermack said:

It seems to be confirmed now, that Omicron causes a less severe set of symptoms, on average. Any suggestions as to why, when it is clearly far more efficient at infecting a host? 

My suggestions are 1) That the raised infectiousness somehow causes a quicker and bigger response from the immune system, resulting in a less severe illness. That might be bad news for people with a weakened immune system. 

2) Maybe the raised infectiousness means that more vaccinated people are catching it, and that they are getting less ill, and therefore affecting the figures. You could check that out, by looking at the figures for the percentage of vaccinated people who are testing positive, and how it compares to pre-omicron times. 

3) Because it's so much more infectious, it might be succeeding in infecting more young people than previous variants, resulting in less serious symptoms on average. 

I would like to see an analysis of how people of my age (71) fare on average, when they catch it, and compare that to Delta etc. 

I don't know why the numerous mutations have had this effect but preliminary reports suggest Omicron does not go for the lungs any more, just the upper respiratory tract, like any other "flu" or cold virus. 

[CharonY]

There are several studies hinting at mechanisms (mostly animal models, I can dig them out, I have them on paper only atm. The one to look at would be Diamond et al. "The SARS-CoV-2 B.1.1.529 Omicron virus causes attenuated infection and disease in mice and hamsters"). There are some other in vitro and animal studies, but in summary it appears that the virus accumulates mostly in the upper respiratory tract and is less effective in infecting the lung, where most of the critical damage is happening. 

46 minutes ago, mistermack said:

My suggestions are 1) That the raised infectiousness somehow causes a quicker and bigger response from the immune system, resulting in a less severe illness. That might be bad news for people with a weakened immune system. 

That actually often results in more issues (e.g. cytokine storm). When it comes to the immune system, perhaps somewhat counter-intuitively a stronger response is not automatically better. It depends a lot on the type of the response. In fact, stronger immune responses have been associated with more severe progression of the disease in COVID-19. In addition, the fact that folks test positive, indicate that the virus has established itself and propagated. If it was cleared early on, folks would remain below the detection limit.

 

46 minutes ago, mistermack said:

2) Maybe the raised infectiousness means that more vaccinated people are catching it, and that they are getting less ill, and therefore affecting the figures. You could check that out, by looking at the figures for the percentage of vaccinated people who are testing positive, and how it compares to pre-omicron times. 

Omicron has shown to reduce protection to infection especially with the AstraZeneca vaccine (where it basically circumvents it without boosters) and reduces infection protection with other vaccines, too. So that definitely affects broad numbers. The issue is that comparisons are not easy, as the vaccination landscape (e.g. boosters), but also reporting methods have changed over time. At this point we need more data from well-characterized cohorts, which are starting to become available.

46 minutes ago, mistermack said:

3) Because it's so much more infectious, it might be succeeding in infecting more young people than previous variants, resulting in less serious symptoms on average. 

Previous variants were pretty good at infecting young folks. But we just did not notice because many had no symptoms. There are huge regional differences (e.g. only testing of symptomatic patients, use of rapid testing etc.) so the data is difficult to compare. A reason why more young people are detected and hospitalized in some areas is likely because omicron is basically sweeping through the population.

 

46 minutes ago, mistermack said:

I would like to see an analysis of how people of my age (71) fare on average, when they catch it, and compare that to Delta etc. 

There are a lot of briefs coming out but so far it has not widely spread among those population (which also is the highest vaccinated group). So far the basic assumption is that it is still high risk until sufficient evidence to the contrary has come out.

Edit: crossposted.

[mistermack]

3 minutes ago, exchemist said:

I don't know why the numerous mutations have had this effect but preliminary reports suggest Omicron does not go for the lungs any more, just the upper respiratory tract, like any other "flu" or cold virus. 

That would be good news. Especially considering that coronavirus was initially identified as "the pneumonia virus". It's quite a change, if it's true. 

I wonder how long it will take to adjust the vaccines to be more tuned to the Omicron variant? We were told ages ago that modern vaccines can be adjusted very quickly. 

[exchemist]

18 minutes ago, mistermack said:

That would be good news. Especially considering that coronavirus was initially identified as "the pneumonia virus". It's quite a change, if it's true. 

I wonder how long it will take to adjust the vaccines to be more tuned to the Omicron variant? We were told ages ago that modern vaccines can be adjusted very quickly. 

Well if this is confirmed we may not need to bother. But let's see. 

But in fact that reminds me of a piece in the Financial Times the other day regarding BioNTech, saying one great advantage of their mRNA method of production is it obviates the long growing time needed by conventional methods. They were hopeful that for example flu vaccines, which have to be changed each year according to the variant forecast as likely to be dominant each winter, could be made fast enough for the variant to be selected at the end of summer, instead of early spring as now. That should allow each year's vaccine to be much more reliably targeted than at present.        

Edited January 3, 2022 by exchemist