How can this new omicron strain have such a high r0 value

it was just upgraded to variant of concern. it’s more infectious than delta which had an r0 or 6-7.

is there an upper limit on how contagious covid can be? this new strain is supposedly up there with the most infectious diseases that exist like measles.

how does a disease go from novel to possibly the highest r0 of any disease in earth so fast? why didn’t other infectious diseases evolve so fast? smallpox never had an r0 this high.

I haven’t seen any information suggesting that any particular R0 value is known at this stage. AFAIK, the concern is that there are some 30 omicron mutations, so as one epidemiologist put it, it has not only some of the concerning attributes of some of the other variants, but some new ones of its own. But my understanding is that these are still being studied, including its transmissibility and potential ability to bypass antibodies. There does seem to be confidence that present vaccines will still prevent severe illness.

There isn’t yet any evidence the vaccines DON’T work against it, so in populations with high rates of vaccination, it should be manageable.

While no strong evidence yet, see this twitter thread:

Actually, the r-naught of measles is 18. This is yet another reason why that disease needs to be eradicated.

Ah old Doctor Doom.
Well he was dead on the money about Delta and falling immunity.

To go back to the question of how high the infective rate (R0) can go, it is driven in part by the viral surface protein(s) and the docking protein on the cell surface. Changes in the virus’ RNA can change amino acids in a surface protein, and when that amino acid change results in a tighter fit with the cell protein, it’s easier for the virus to enter the cell. Easier entry means the minimum infectious concentration (MIC; how many viruses are needed to establish an infection) goes down, making infection transmission more efficient. I saw this happen with the H1N1 2009 pandemic flu virus in a lab I worked in way back when.

Absence of evidence they don’t work doesn’t mean they do.

fair enough, but what I’m wondering is why is covid 19 capable of being so infectious.

a higher transmission rate is a very important survival mechanism of infectious diseases. but smallpox has existed for as long as recorded history, possibly longer, and the r0 is roughly equal to the r0 of delta covid which had only been evolving for a year before delta was evolved from the original covid-19.

I saw an article where it was said that omicron could be five times more infectious than delta.
how is it possible that we have all these other infectious diseases whose r0 never approach these numbers despite them evolving for thousands of years?

Evolution is stupid. By default, it optimizes for growth of the population count. When you do that, you inevitably exhaust your environment of resources and self-destruct. In this case, a few lower energy, more chill varieties of the species are there to catch the resources when they grow back, while most of the high energy varieties die off. If the chill guys are too slow and the resources grow back fast enough to become plentiful again, then more high energy varieties will emerge from the population again - but they’ll be less able to go crazy high energy because things are still growing back and will deplete faster, and these guys are the descendants of slouches. When the resources deplete again, again it will be lower energy guys who survive but - probably - ones who are slightly higher energy than the previous generation of chill folks because the run to exhaust everything was a bit slower this time.

This sort of cycle repeats until a strain is found that has it just right to reproduce at a sustainable rate relative to the reproduction rate of the available resource supply.

I do wonder if any part of that is if it is less symptomatic.

If it doesn’t make you feel as unwell, then you are less likely to stay home, therefore, spreading it more.

Yeah but most cases of flu are asymptomatic and the flu has an r0 of 1.3

I’m leaning towards the hypothesis that we do have a lot of other infectious diseases with high r0.

Evidence: my county, and the schools in my county, have been masking and doing ventilation and having a fair amount of outside time. There’s been no covid transmission within the school, though we’ve had a handful of single cases. But my kids have brought home at least three colds since school started! And apparently there is increasing resarch and evidence these days that a lot of colds are actually carried through the air rather than through formites?

There are some early reports that the omicron variant might be producing a milder illness.

It’s way to early to draw definitive conclusions, but that could be a factor.

They’re respiratory diseases, so again I ask how could they not be mostly transmitted via air vs fomites on surfaces? It’s baffling that so many scientists seem so utterly stuck on that air droplet size theory from many decades ago and insist we much be getting sick from out shameful instinct to touch our faces rather than breathing it in.

The R0 of COVID is likely to bounce around a bit for the following reason: the virus is an RNA virus, and must make a back-copy of DNA in order to make more RNA for packaging. That process is inefficient and introduces many errors in the form of changes (i.e., mutations) in the DNA. For viruses that can tolerate the DNA changes, some changes may alter how the spike protein fits into ACE2 cell receptor, and how tightly it is held. Different viruses use different cell receptors on the cell surface to enter the cell, and those receptors vary in concentration and location among various body tissues. COVID has evolved to attach to the ACE2 protein, found in large concentrations in lung and throat cells. That is a very efficient means of infecting and spreading by aerosols and droplets generated by breathing, coughing, and sneezing. For contrast, HIV attaches to CD4, found mostly on blood cells, and is poorly transmitted by aerosols and airborne droplets.

Viruses in general are termed successful or unsuccessful, based on how sick they make the host. CMV is a very successful virus because it normally causes asymptomatic or very mild symptoms, and the host can easily spread it around. Ebola, OTOH, is not very successful because it kills the host before the host has a chance to spread it very far. RNA viruses ride along a razor’s edge, where a few mutations allow them to be successful and many others make them unsuccessful. Thus there is evolutionary pressure to adapt to the host to minimize the host respone and maximize the shedding that releases the virus to other hosts.

And there are a whole bunch of other scientists yelling at that first group of scientists to switch their recommendations to things effective at fighting airborne viruses.

Part of the resistance to switch away from droplets to airborne is political, for lack of a better word, because droplets are easier to deal with. A place wipes down surfaces and has a sneeze guard in place, and they’ve done what they can, and it is obvious something is being done. Airborne requires filtration and ventilation, which can be much more expensive to implement. They also operate in the background, so they aren’t as clearly “doing something.”

According to scientists who sequenced omicron, it seems to have picked up some genetic material from a coronavirus that causes the common cold. So, think in terms of that level of infectiousness.

That doesn’t make sense. Delta’s R0 is 6-7, and the common cold’s only 2-3. Isn’t Omicron supposed to be twice as infectious as Delta? How would adding genetic code from something no more than half as infectious cause it to be twice as bad?

The common cold is caused by a bunch of different viruses, so that’s presumably an average. I can’t find an R0 for just coronavirus colds. But I’m not vouching for the reasoning, either.