It would seem that the most active and out going would be first to catch the virus and the also the ones most likely to spread it. Once the first 10% of the most active catch it and quickly pass it on to those close you might expect a quick infection of about the first 50% of the population. After the initial wave could we expect a dramatic slowdown?
We’re several months into this and official numbers are that 1/4 of one percent of the population has it in the US, so I’m not sure what your numbers represent. It’s highly probable that the actual number infected is drastically higher than official numbers, but I’m not aware of anyone who thinks we could be near 50% at this point, so what do you consider “quickly” and what point are you trying to make?
If you really do want to know about herd immunity, if we start with an R[sub]0[/sub] of 3.5, we reach the threshold when 72% of the population are immune. The formula is (R[sub]0[/sub]-1)/R[sub]0[/sub] (sorry, no LaTeX in the formatter here). We aren’t sure if 3.5 is the correct number and we certainly aren’t sure if previous infection grants 100% immunity, but that gives you an idea of the kind of target we need to hit.
! would consider quickly about 6 months with no controls. My point is I was kind of looking for that magic number where death rates would fall into numbers similar with an annual flu. With strict controls and no vaccine I could see this going on for years and years.
I don’t think we have enough information to know any of that.
- What percentage of those exposed become immune?
- How long does that immunity last?
- Can the virus mutate in a way that bypasses immunity (Influenza does, but measles does not)?
If the answers are >90%, many years, and no, then once we all get it or a vaccine, the pandemic ends and will be much less of an ongoing threat than the flu. But if the answers are <30%, a few weeks, or yes, then we will be in facing a much different new “normal”.
With strict controls, no vaccine, possible temporary immunity with recovery from infection, plus the fact that coronaviruses mutate notoriously, you can see why the infectious disease experts and epidemiologists are probably scared shitless.
~VOW
Way too many unknowns to give a magical number, but if I understand it correctly the problem is letting things go wild quickly overwhelms the medical system. Early on, it was reported that in China, the mortality rate in Wuhan was something like 5% but in other parts of China, the mortality rate was 1%. It was explained that in Wuhan, the medical system got overwhelmed and was not able to handle all the cases. The same thing happened in China.
Only looking at the number of Americans 65 and older, there were about 50 million in 2017. If 50% of them become infected then a 5% mortality rate would kill 1.25 million of them. There simply isn’t a way for the US medical system to deal with that number of people.
For herd immunity, cattle pack together tightly, nose to butt, inhaling deeply. Weaklings and rejects are left at the outside of the pack for predators to pick off. The most valuable innermost critters survive. There’s a human cultural metaphor here.
The other herd immunity has X% of the populace infected and recovered, or inoculated, so they are not contagious. Do we know whether this works with COVID? Has human-COVID herd immunity been verified yet or is it still at the “wishful thinking” stage?
Of course there is not proof of what has not yet had a chance to occur, but to the degree that the past informs the future, that we expect to experience the sun rising tomorrow because it rose today, and yesterday, and the days before that, some impact of herd immunity is expected at some point. That is not wishful thinking.
If your understanding is that the concept only applies if an individual in the Recovered bucket is 100% not susceptible, or that the protection needs be lifelong, then that is a misunderstanding. Less complete protection to each individual from recovery would require more to be in the Recovered bucket is all.
There is no real question that infection (and possibly at some future point immunization) will provide some degree of resistance to new infections for some period of time. How big the values of those “somes” are is unknown. If like the long established common cold causing coronaviruses then maybe only for 1 to 3 years and maybe not 100% for anyone even at the start. If like SARS or MERS much longer. If the germ mutates very quickly then maybe shorter.
HoneyBadgerDC the “magic number” depends on information that no one has, and circumstances that vary, and on how the specific assumptions that any specific model uses actually apply to the specific real world circumstance.
You need more in the recovered bucket with greater degrees of infection resistance for a very contagious bug in very crowded highly mixing circumstances, than you do if the germ is less contagious OR if the circumstance one less prone to giving it as many chances to spread.
And the mortality rate along the way depends on which risk group of the population is the group that gets the chance become infected and then either to join the recovered or die, vs those who more likely to remain as susceptible but are subsequently relatively protected by virtue of being less likely to be exposed.
Sorry if I am not expressing that as clearly as it could be.
- What will it take to achieve herd immunity with SARS-CoV-2?
As with any other infection, there are two ways to achieve herd immunity: A large proportion of the population either gets infected or gets a protective vaccine. Based on early estimates of this virus’s infectiousness, we will likely need at least 70% of the population to be immune to have herd protection.
[ul]
[li]In the worst case (for example, if we do not perform physical distancing or enact other measures to slow the spread of SARS-CoV-2), the virus can infect this many people in a matter of a few months. This would overwhelm our hospitals and lead to high death rates.[/li]
[li]In the best case, we maintain current levels of infection—or even reduce these levels—until a vaccine becomes available. This will take concerted effort on the part of the entire population, with some level of continued physical distancing for an extended period, likely a year or longer, before a highly effective vaccine can be developed, tested, and mass produced.[/li]
[li]The most likely case is somewhere in the middle, where infection rates rise and fall over time; we may relax social distancing measures when numbers of infections fall, and then may need to re-implement these measures as numbers increase again. Prolonged effort will be required to prevent major outbreaks until a vaccine is developed. Even then, SARS-CoV-2 could still infect children before they can be vaccinated or adults after their immunity wanes. But it is unlikely in the long term to have the explosive spread that we are seeing right now because much of the population will be immune in the future.[/ul]*[/li]
It should be noted that for some infectious diseases we’ve never developed natural herd immunity through exposure. With varicella zoster (the virus that causes chickenpox) we had regular epidemic outbreaks in children prior to the development of a vaccine despite the fact that exposed adults were (practically speaking) immune from new infection, and nearly every person on the planet got the disease. Fortunately, serious morbidity and mortality in chickenpox is exceeding rare, and aside from the small minority or people who suffer from shingles, there are no lasting consequences from the disease beyond a few shallow pockmarks.
There is, of course, no natural herd immunity from influenza Type A and B because the viruses mutate and recombine so frequently to defeat natural immune response, but the ~30% of people who are inoculated with the annual vaccine provide enough suppression to prevent epidemic outbreaks in most years, and even the epidemics that occur (P & I mortality for the 2019-20 flu season slightly exceeded the epidemic threshold even before SARS-CoV-2 was circulating) are never severe enough to require general quarantine or for governments for issue special restrictions.
So herd immunity–through vaccination (hopefully) or exposure (which will require many hundreds of thousands of deaths in the US, and on the order of 10 million deaths worldwide)–is not a strategy for controlling the pandemic but rather the threshold we’ll achieve once we’ve managed to do so. And if the virus mutates rapidly or the immune response is not robust and long-lasting, then we may not attain herd immunity without periodic vaccination.
Fortunately, this decease seems to rarely exhibit severe presentation in children, so we’re not seeing swaths of kids becoming severely ill or dying, which would have devastating future consequences as polio did. However, we are seeing younger adults (down to the 20s and 30s) presenting atypical blood clotting and organ failures without a clear mechanism, which is very concerning because we just cannot predict who is at risk on an individual level or how the virus could mutate to become more virulent or reinfect people with prior exposure and prompt hypercytokinemia and uncontrolled inflammation.
Stranger
Herd immunity can be understood in terms of our old friend R.
R gives us a metric on the chance that an infection can make it from a single infected person all the way to you. R is composed of a number of parameters, especially:
[ul]
[li]The chance that an encounter by a susceptible person with an infected person results in infection.[/li][li]The rate of interactions (which is obviously dependant on lots of things)[/li][li]The likelihood of a person being susceptible.[/li][/ul]
Right now, most people are susceptible, and we are trying to drive R down by reducing interactions. and a bit of reducing chance of infection.
But even now, if you imagine where you are and where there is an infectious person, there is a path the infection needs to take jumping from person to person to get to you. Every jump is governed by chance. In an unrestricted environment (without social distancing and protective wear etc) it is the infectiousness and the chance that the next person interacted with isn’t susceptible that governs the spread. If say half the population aren’t susceptible and the chance of passing on the infection is 50% at an interaction, and an infected person interacts with four people whilst infectious, on average the disease spreads to one person. R = 1. If now 75% of the population are not susceptible there is a lower chance of infecting anyone, and on average an infectious person now has a 50% chance of infecting anyone whilst they are ill. R< 1 and the infection damps out. Each day fewer people are infected, and fewer people become infectious.
You could be really unlucky, and be at the end of a chain of infectious encounters. Like getting a run of heads on coin tosses. But as the number of susceptible people decreases, that chance of a chain of infection occurring drops, and it drops fast. A run of five heads is one in 32, a run of five sixes on a die roll is nearly one in 8000. Corvid-19 seems to be not especially infectious - the chance of catching it on a single encounter is not nearly as bad as say chickenpox (which is essentially so close to 100% it hardly matters). So we don’t need as many people in the populace to be immune to create an effective damping out of community infection as for say chickenpox or measles.
Once you have a nice proportion of resistant people in the populace, if a new infected person arrives, the chances are that, even if they did encounter some susceptible people, the infection would quickly damp out, and would not make it to many of the remaining susceptible people. Which is how we rely on large scale immunisation to protect those few that for medical reasons can’t be immunised, and why for really infectious diseases (ie measles) we get into trouble when the number of immunised drops even a bit (due to say antivaxxers.)
Interestingly even chickenpox illustrates an important point here. Thing is that primary chickenpox infection did every year cause some number of more serious illness and a smaller but real number of deaths. Almost all of them were in adults and very rarely in kids younger than preteens.
There were always some individuals who reached adulthood never having gotten chickenpox, who if they got chickenpox as adults would be at very significant risk of severe morbidity or death. Many of them avoided it as adults because most of those around them were immune from childhood infections.
Lots of people getting chickenpox as adults would have a huge mortality rate. Nearly 100% getting it as children led to a very low mortality rate, and provided some protection to susceptible adults (although some were still exposed when their kids got the disease). You really did not want to avoid chickenpox as a child before the vaccine was around as getting it when younger was the much better option.
I don’t think anyone can, with justified confidence, say how many deaths will or won’t occur due to COVID-19 with or without any specific social distancing interventions.
What on can say with confidence is that as various bodies “relax social distancing measures when numbers of infections fall” it will be important to do so in a way that concentrates whatever infections occur, and some finite number will occur, to the lowest risk groups to the greatest degree possible, keeping hospitalization (and death rates) as low as possible even as the resolved bucket grows to whatever degree it does while keeping those rates within some acceptable parameters.
There is still inadequate planning in place for how to best *protect the most highly vulnerable populations for the very long haul *this will be, as social distancing measures are gradually relaxed. And note, even a vaccine does not assure they will no longer be vulnerable; many vaccines help get society closer to herd immunity levels yet still leave vaccinated elderly individuals vulnerable on an individual basis as they commonly respond less well to the immunization. And no one should state with confidence that they know when or if a safe and effective vaccine will be available and ready for wide spread use.
The big challenges -
Congregate living of elderly and other high risk populations with care workers and fellow residents who can be contagious when a- and pre-symptomatic.
Multigenerational households and close contact extended families with elderly or otherwise high risk members. Many poor communities (and not just urban minority ones but certainly including them) have an over-representation of this circumstance and as diabetes, obesity, hypertension, smoking, etc., are also over-represented the challenge is huge.
Minimizing and balancing the harms of long term social isolation that protecting them engenders, both real mortality risk and to quality of life.
DSeid, I have asked this question on other threads but haven’t received any responses on it. Is it possible that the extremely high death rates in New York could be a reflection of a healthcare system that tends to stretch out lives a bit longer than most countries. Not to be confused with life expectancy which is an entire different issue. I will be getting my test results back today hopefully. I feel I am recovered now from this virus but have yet to verify that I have it for sure.
If I understand what you are asking (and not sure I do) I do not believe that such is consistent with the numbers.
What I am asking is that at any given time would the U.S. or Possibly New York have a considerably higher population of people in an extremely vulnerable condition. This could be for any number of reasons unique to the U.S.A. But the question was more about our healthcare system extending lives longer than most countries might.
Agreed; I was just basing those figures on an assumed infection fatality rate of 0.3% to 0.5%, but due to both a lack of comprehensive testing, and uncertainties in the completeness of reporting deaths directly attributable to COVID-19, we just don’t really know what that is. I suspect (and hope) it is less than the 1% to 2% that was originally estimated, but even a 0.1% IFR would result in a million deaths directly worldwide, and far more in subSaharan Africa and developing nations in Asia and South America where other co-morbidities such as AIDS and tuberculosis, seasonal epidemics like malaria and Dengue fever, and general breakdown of fragile medical support and social services will result in even more ancillary deaths. Some of the rough estimates I’ve seen for Africa this summer look dire, but we’ll see how those pan out.
To add to this, identifying the apparently healthy, working-age people who are unknowingly at risk of severe morbidity or mortality. Even if that is only a fraction of a percent of the middle age population, once it flares up (as I expect it will with states in the US that are lifting isolation measures even as their death rates are still rising with restrictions in place) people are going to be fearful about attending public events, working in large “open office” spaces and cubical farms, and taking public transit. Being able to predict who is immune and who is likely at risk will at least result in a middle population of people who feel comfortable resuming something like normal life even if they have a significant chance of contracting the virus. And if infection rates in NYC reflect actual trends, only ~15% of people in the US have even been exposed and may have a (still unknown) degree of immunity.
You seem to be of the impression that the United States and NYC in particular have a more vulnerable (i.e. more elderly) population. This is simply not true. The US is 40th-something in terms of life expectancy across all estimates (CIA World Fact Book: “Life Expectancy At Birth”) and New York City proper has a median age in the mid-30s (Barach College Weissman Center for International Business: “ New York City (NYC) Population Estimates By Age, Mutually Exclusive Race and Hispanic Origin, and Sex”) with a much smaller elderly population than the nation as a whole and particularly the rural Midwest. Estimates of how many older people are in a state of poor health or have co-morbidities vary depending on your assumptions but in New York City walking and climbing stairs are a part of daily life for most people which means they are likely getting more exercise and are in relatively better health than people elsewhere in the country.
Our healthcare system is not particularly good at “extending lives longer than most countries might” if by “most countries” you mean virtually every developed democratic nation with some form of universal health care system, although we are much better than, say, Azerbaijan, Honduras, or Eritrea, so there is that. Of course, Americans tend to have a lot of chronic health problems due to lifestyle choices such as obesity, smoking, lack of exercise, et cetera, but the same is true in many countries around the world and do not explain mortality rates in toto. Iran, which has an almost negligible percentage of population over 65, had such high mortality rates that satellite imagery showed them digging mass graves and anecdotal reports had hundreds of people dying every day when the US was still seeing single digit deaths.
Stranger
The question had nothing to do with life expectancy as I stated in my post. Life expectancy and extending lives don’t have to be related to one another. Treating people only when they get sick might extend a life that could have been in much better heath at the same age . The reason I am suspecting that we might have an unusually large vulnerable population is because of the high death rate we are seeing in New York. I do agree with you about the life style choices and that may be the primary reason.
Life expectancy is related to care of and treatment for chronic illness. It is true some populations have lifestyles that increase both life expectancy and quality of life through fewer chronic illnesses such as heart disease, hypertension, diabetes, and COPD, but these are relatively small populations like Okinawa, and the national demographics are more strongly correlated with better medical intervention and nutrition in general.
I cannot parse the statement, “Treating people only when they get sick might extend a life that could have been in much better heath at the same age.” I am guessing that what you mean is that countries with more advanced medical technology and egalitarian health and social support systems will tend to care better for older patients with co-morbidities but it has been well established that the health care system of the United States does not excel in that measure.
As has been pointed out numerous times in other threads in which you have been a participant, the COVID-19 disease is not just striking at people who are elderly or who have underlying illness. Although there is a correlation with mortality and hypertension, which is to be expected because hypertension exacerbates illnesses and health challenges in general, there are people in apparent perfect health in their 50s, 40s, and even in their 30s and 20s who are presenting severe morbidity and often rapid and unexplained mortality. This isn’t simply like a normal flu that causes already sick people to contract serious pneumonia and succumb; the COVID-19 disease itself has an inherent mortality that is killing people with no underlying conditions in ways that are not well understood.
Stranger
It’s becoming more and more clear that “herd immunity” has become a right-wing buzzword that means ‘send the poors back to work so the 1% may start making money again.’
Practically (as opposed to sophistically) speaking, there is no herd immunity to the common cold. There is no herd immunity to influenza. We know that ‘herd immunity’ isn’t guaranteed for any virus.
Yet in recent weeks, the right has been trumpeting Herd Immunity as the miracle that could Put Everyone Back To Work—despite the complete absence of any evidence that this might be so. Scientists are warning that we have no idea how many people who’ve had COVID-19 might be susceptible to getting it again----but that fact is being completely ignored by the rah-rah-put-the-peons-back-to-work crowd.
Notice that not one of these cheerleaders for ‘let’s increase the rate of infection so we’ll (Definitely!) get Herd Immunity,’ have volunteered to step up to the front lines themselves. None of them are putting themselves in harm’s way. They are only advocating that risk for others.
As implied here, this is yet another predictable talking point of the right: that only the Sick and Old are at risk. This lie is a vital component of the right’s argument.
That’s right. And it’s a fact that the right will continue to ignore, in favor of their Let’s Get Herd Immunity, it’s Easy! propaganda.
I don’t believe there is much to support the idea that New York has an especially high number of those who are particularly vulnerable due to having their lives extended while continuing to be ill (compared to other cities, states, or countries that have been impacted). Demonstrating that would be the first step of supporting your hypothesis. Failure to see that would falsify it right there.
While I know that everything becomes partisanly tribal in today’s America, it is possible to discuss the idea devoid of consideration of which team seems to promote it the most.
FWIW here’s an analysis from Israel proposing a series of “controlled avalanches” which argues that building to herd immunity in a very controlled manner would save lives.
EVERY model used for decision making has to make certain assumptions. This one has three big ones.
They assume that immunity from SARS-CoV-2 is longlasting. Might, might not be. Consensus of most experts though is that 2 to 3 years minimal is a reasonable assumption, and that would be enough to highly likely get us to a decently safe and effective vaccine.
They assume that the period of infectiousness is limited. Most would accept that one.
They assume that IFRs are low for those 20 to 49 without known comorbidities (although I can’t be sure it looks like that are using for patients aged 20-29,
30-39, and 40-49, 0.03%, 0.08% and 0.16% respectively.)
It’s then a proposed waves of volunteer group exposure and quarantine of those low risk by age and lack of known other risk factors. The whole process is modeled as taking 210 days and, using these assumptions, would greatly reduce mortality.
The easy criticism is to argue against the assumptions used. But again all the models make assumptions and these are pretty realistic ones.
For what it is worth, while I would not qualify under the model above (too old and history of asthma), I would have no problem volunteering for such a program of controlled infections. And better me than someone at higher risk. I personally accept that as a provider I am going to get the disease at some point and it might as well be before I get any older and while business is slow!