Is there any information on what the upper bound might be on the infectivity of SARS-CoV-2? I think a lot of people just assume one big jump consumes most of the range, but we've seen at least three big jumps so far ("Doug", "Alpha", and "Delta").
> And you can imagine, it was quite a mouthful. So, we started to call this D to G mutation ‘Doug’, and then any of the other virus sequences that didn’t have this mutation … we called ‘Douglas’, so it was sort of a bit of a private joke within the lab,” she said. “As more mutations came about, we’d come up with a person’s name for them.”
This is getting at “saying the quiet part out loud.”
For a variety of reasons media and influential organizations have avoided considering the upper bound on virility and mortality (? Not sure the right term) of covid.
But to think delta is it would be some kind of miracle. It would mean we are going through the worst of it, and that after we handle delta globally, people can worry about other things.
But it doesn’t stand to reason that we are done here with covid. There are too many hotspots and I believe delta is older than most of the big ones right now.
How likely is a nasty new variant not pop out of Iran or India, or Texas?
What about variants created by non-human beings like rats? [1] Are we going to skate by on those? That would be great!
I suspect the public is not ready to fully address the breadth and depth of covid’s impact. I also speculate that the “booster” shot suddenly being prescribed is intended to help ward off future variants as much or more so than delta alone.
You probably mean "virulence", not "virility". The latter word denotes the masculine ability to procreate.
The confusion arises because the Latin word "vir" means "man" (specifically of male sex, as opposed to human), and the similar word "virus" means poison.
SARS-CoV-2 has multiple animal reservoirs, and that's one reason why it will be impossible to eradicate. But generally variants that evolve in animals will select for fitness in those different species. So those will probably have less impact on humans.
This is one piece of circumstantial evidence why some virologists suspect the virus was produced in a lab doing gain of function research using transgenic mice with human like respiratory systems. When the virus first appeared in Wuhan it was already really good at infecting humans. That would be unlikely if it had evolved in wild bats or pangolins and then jumped straight to humans. But we don't know for sure, maybe it was just natural bad luck with no lab involved.
> When the virus first appeared in Wuhan it was already really good at infecting humans. That would be unlikely if it had evolved in wild bats or pangolins and then jumped straight to humans. But we don't know for sure.
Just curious about this point - wouldn't this always be the case, since before it was good at infecting humans it would only be in a few if any of them? IE. My thinking is that even if it had existed for a while before that point, we'd be unlikely to know since it wasn't at that point good at infecting humans and thus not many had it.
SARS-CoV-2 is a generalist that can infect many animals. I doubt it a "lab leak". Studies of genetic sequences from around the Wuhan fish market showed that it had been circulating and mutated a bit for some time before it was detected.
Here is a fantastic resource from the UK government that answers your question in great detail [1].
> As eradication of SARS-CoV-2 will be unlikely, we have high confidence in stating that there
will always be variants.
> We describe hypothetical scenarios by which SARS-CoV-2 could further evolve and acquire,
through mutation, phenotypes of concern, which we assess according to possibility.
> Scenario One: A variant that causes severe disease in a greater proportion of the population than has occurred to date. For example, with similar morbidity/mortality to other zoonotic coronaviruses such as SARS-CoV (~10% case fatality) or MERS-CoV (~35% case fatality). [...] Likelihood: Realistic possibility. Impact: High.
> Scenario Two: A variant that evades current vaccines. [...] Likelihood: Realistic possibility. Impact: High.
> Scenario Three: Emergence of a drug resistant variant after anti-viral strategies. [...] Likelihood: Likely - unless the drugs are used correctly. Impact: medium.
> Scenario Four: SARS-CoV-2 follows an evolutionary trajectory with decreased virulence. [...] Likelihood: Unlikely in the short term, realistic possibility in the long term.
And here is one very relevant quote:
> There is no historic precedent for the mass administration of antiviral medication in the community as prophylaxis, apart from the use of anti influenza Neuraminidase Inhibitors, which were used to a limited extent in this way in the early phases of Influenza Pandemic of 2009 in the UK. The safety and efficacy profile must be extremely well established for a mass administration strategy to work and poor compliance will likely rapidly lead to the selection of drug resistant variants, rendering such a strategy short lived.
[1] Can we predict the limits of SARS-CoV-2 variants and their phenotypic consequences?
> It may already be getting harder for SARS-CoV-2 to make big gains in infectiousness. “There are some fundamental limits to exactly how good a virus can get at transmitting and at some point SARS-CoV-2 will hit that plateau,” says Jesse Bloom, an evolutionary biologist at the Fred Hutchinson Cancer Research Center. “I think it’s very hard to say if this is already where we are, or is it still going to happen.” Evolutionary virologist Kristian Andersen of Scripps Research guesses the virus still has space to evolve greater transmissibility. “The known limit in the viral universe is measles, which is about three times more transmissible than what we have now with Delta,” he says.
Measles is estimated to be about 300% more infectious than the delta variant, so if it surpassed measles it would be the most contagious viral disease known to man. It's already pretty close to what is assumed to be the "ceiling".
I'm not sure "only twice as bad" paints an accurate picture.
- Herd immunity is much harder. Calculated as 1 - 1/r0 where r0 is defined in relation to transmissibility. So if r0 = 3 that's ~66% need to be immune to stop the virus. If r0 = 6 that's 83% needed, much higher threshold.
- The virus is only getting more deadly. A preprint study found delta has "120% greater risk of hospitalization, 287% greater risk of ICU admission and 137% greater risk of death"[1]
Also 225% more transmissible is 3x more unless I'm doing my math wrong?[2]
Right, and that's where vaccine efficacy comes into play. If r0 is 6 and HIT is 83.3%, but efficacy is only 90%, then you actually need about 93% vaccinated.
And for herd immunity, what matters is transmission, and the vaccine efficacies for asymptomatic infection are pretty low; 50-60%. So mathematically impossible without severe lockdowns and/or improved vaccines that are better at preventing transmission.
But I've been operating under the assumption that while vaccination won't prevent you from infection, it is still highly effective (90%+) at reducing symptoms, even with Delta. I'm certainly open to learning if this is false, however. I've just seen statistics that over 95% of people hospitalized are unvaccinated.
There are many efficacy numbers. mRNA does help against infection but efficacy is apparently low, like 50-60%. Makes sense because they weren't really developed with that in mind.
Efficacy goes to 60-80% for symptomatic, over 80% for serious/hospitalization, and mid 90% for death. I think.
Herd immunity happens long before we are all infected. Less than 40% of the US population is completely unvaccinated, which means we can open up more without overwhelming hospitals. That does put the unvaccinated at increased risks, but the general public is seemingly unwilling to continue lockdowns to protect people choosing not to be vaccinated.
If ~85% is needed for herd immunity then we could be rapidly approaching that point. Though specific locations would likely have outbreaks even if it was less of a concern nationally.
With an R0 of about 6 for the Delta variant, herd immunity won't provide a meaningful level of protection for most people. Herd immunity works with less contagious diseases because susceptible individuals can go their whole lives without exposure. But with SARS-CoV-2 now being endemic worldwide we'll all eventually get exposed, it's just a question of when. So the smart move is for everyone to protect themselves by getting vaccinated and actively treating co-morbid conditions like obesity, diabetes, hypertension, and hypovitaminosis D.
Any further lockdowns at this point cause far more harm than benefit.
They can prevent hospitals from being overwhelmed. Opening or not opening schools are one case where local communities are going to adjust based on the rates of hospitalization.
There's math you can do to roughly judge impact of partial vaccination. If R0 is six, and you're looking at hospitalization, estimate vaccine efficacy for Delta at around 90% (I've seen estimates above and below that).
Taking your estimate of a 60% vaccination rate:
6 * (1 - (.6 * .9)) = 2.76
2.76 is the effective Rt, which is far above 1, so no, that is not enough to open up more without eventually overwhelming hospitals.
Natural immunity from catching COVID, and other (inherently temporary) mitigation measures like masks/distancing/lockdowns would bring that Rt down further. But clearly what is best is more vaccination.
2.76 assumes normal conditions, social distancing literally changes the equation.
Mask use for example pushes that down. It’s easier to get below 1 with a 50% vaccination rate than a 0% rate. Meaning we can open up more without overwhelming hospitals.
That's pretty much what I said in my last line. The problem is, "opening up more" generally tends to mean things like less masking and less social distancing. So to the extent that Rt is pushed down by mitigation measures, Rt gets pushed back up when those mitigation measures end.
The advantage in my mind is you can avoid the most costly mitigation strategies.
Unfortunately, vaccination rates are age dependent so opening schools is a very high risk activity. Children are at low risk for COVID but they would be a major vector for transmission as everyone under 12 is unvaccinated.
That’s quite regional. Nationwide there is still plenty of ICU beds available, and presumably if it gets bad enough hot spots will respond appropriately.
By moving people with covid to other states, or importing medical personnel and equipment. Do so aggressively enough and you can keep capacity available.
And then you'll eventually realize: having thousands of people getting intensive care at the same time until everyone either had it or died from it is moraly not acceptable. Why do you come up with the idea that it's better to increase capacity rather than using large scale vaccination efforts?
I think there's am R0 for initial strain and then ranges for the other variants. I thought it was in Wikipedia but either it's been edited out or I saw it elsewhere.
What I recall (so huge grain of salt here) was R0 at 2.3 for initial strain then around 2x for Alpha and another 2-3x for Delta. Not. Great.
"Furthermore, measles's reproductive number estimates vary beyond the frequently cited range of 12 to 18.[15] The NIH quote this 2017 paper saying: "[a] review in 2017 identified feasible measles R0 values of 3.7–203.3"
Do absolute R0 numbers have meaning without a specified environment?
As in, shouldn't there be various values for R0 within a fully vaccinated community, R0 within an age group, R0 relative to the prevalence of active infection in a community, etc.?
I'm just wondering what complexity is concealed within an R0 figure. After all, if every infected person really infected 6 other people every 2 weeks or so, it would infect every person on Earth in about a year and a half.
Which is probably why R0 is distinguished from R1. Since otherwise R1 would be R0**2, and I highly doubt it is. It could be higher if viral load was a large factor (you have x% chance of picking it up when around a single carrier, but >x% if surrounded by multiple). Far more likely, it would be lower as it burned out tightly-connected groups.
Anyway, just thoughts triggered by seeing absolute R0 values.
Consider R0 a rough estimate of how many people each cade infects. It's an imperfect instrument but helps communicate the idea clearly that answers "how infectious is this virus?"
the next big mutations may not be more infectious because they can survive outside the body longer, but because they get around existing immunity or theres a longer asympomatic-but-still-transmissible phase. theres a lot of different paths this could take to mass infection.
