One possible explanation for the sharply dropping number of cases in the USA is that there has been a change of government
Discounting that, another possibility is that everybody is just better behaved. Could be, but it’s not the only possibility: and it disregards the fact that early outbreaks were associated with meat-packing and aged-care facilities.
So perhaps it’s just that everybody in meat-packing and aged-care facilities is better behaved.
Or perhaps part of the explanation is that the USA has achieved herd immunity in high-risk populations.
That is, ‘high risk of transmitting the disease’, not ‘high risk of dying or hospitalization or anything else’.
Or even, at the top estimates, 1/3 of the USA has already had COVID, and perhaps, taking into account disease differences, that’s enough for effective herd immunity.
I’ll note that in Australia, where there has been contact tracing, the common behavior of the index cases has been quite different than majority community behavior. The fact is, a lot of people haven’t been to a dozen bars, restaurants, clubs and parties in the last two weeks.
So, what do ya think? Does anybody think that COVID in the USA is just leveling out anyway?
The confirmed case count in the US is 27 million, which is less than 8% of the population. Even going with your 1/3 estimate we’re still a long way off from herd immunity.
What I think we’re seeing here is the natural ebb and flow of a pandemic. What appears to be happening is that we are coming out of the 2nd wave. I say appears, because we wont know if this is just a temporary down turn for a while yet. If we are on the downside of the second wave it will soon level off. The reason for the second wave is that the virus had spread to exploit vector rich environments. Now that it’s picked of most of the “low hanging fruit” in those environments, it has to work harder to spread and thus slows down some. What we should see is a series of flare ups as the virus makes its way into communities that have thus far been relatively spared. And as communities let down their guard due to a false sense of security at seeing the infection rate drop as it is.
We’re still a long way from safety. In order to reach anything like herd immunity, we’re going to need at least 250 to 300 million people to have some form of immunity. If we reach the govt’s goal of a million vaxes a day that’s still 9 months away.
I wonder if the segment of the population that has ignored any precautions is approaching herd immunity. Most of the rest of us are just careful enough to have avoided it.
well, it’s not really herd immunity. But, yeah, we’re likely to see communities where the infection rate drops extremely low due to a lack of targets. But very few communities are truly isolated and therefore the virus will always find a way.
Misuse of the term herd immunity, but a few things may be going on here. One is the quick and easy vector paths have been already exploited by the virus, the well connected, (many points of close contact that happen often) people have already spread the virus through their networks. Slower networks take longer, populations with less contacts, less interconnected networks and less close contact, and those taking greater precautions. The vaccine is being deployed, and though it is disputed if a vaccinated person can be a carrier, it most likely acts like a partial stop for spreading, sort of a circuit breaker along a path. Far from herd immunity, what I believe we are seeing is network fragmentation with the virus having a harder time spreading from group to group, thus slowing it.
What is required with herd immunity is that the infection rate per person must average below 1 and stays there even when the virus hits a mostly uninfected network, this way the virus can not prosper and every new infection hurts the virus further in its efforts to infect new hosts. This is highly unlikely with a population with a low percentage of vaccinated people, and even more so with a population trying to actively avoid the virus (unless that active avoidance becomes the new norm in the society going forward). All those last 2 will do is delay the outbreaks, which will come in waves, this is not herd immunity, but exactly what we are seeing now.
So no we are not near herd immunity, but are somewhat controlling the outbreaks. That in itself is good, as we wait for vaccines and develop better medical treatments, and keep hospital and ICU beds open for those in need.
The unmodified basic replication number, R0 (i.e. the mean number of replications per infection) of the original SARS-CoV-2 virus has been estimated at between 3.8 and 8.9, which makes the estimated heard immunity threshold to between 74% and 89% without social and physical modifications to reduce the incidence of transmission. The B.1.1.7 variant has an increase in infectiousness of between 40% and 70% which implies the adjusted herd immunity threshold is between 81% and 94%. Other rapidly spreading variants are believed to have an equal or greater R0 value.
It seems to have become an assumption that if we just let enough people get infected we’ll achieve some theoretical herd immunity threshold, although these assertions seem to most often be made by people who have no idea what herd immunity is or how it is actually achieved. There are, of course, many diseases such as mumps, measles, and chickenpox that are so transmissible and infectious that they never achieve any herd immunity and have continued to circulate in human populations for centuries if not millennia. Even smallpox with its relatively modest R0 of between 3.5-5.0 never achieved herd immunity globally and continued to ravage through populations until modern public health methods were instituted to control it and a massive global vaccination campaign was launched to eradicate it.
This is notwithstanding the fact that the SARS-CoV-2 virus is mutating at a rate faster than expected (not quite as fast as Influenza A but fast enough that we can expect to see multiple variants with resistance to previous inoculation have arisen within a 12 month period) and because of its almost uniquely asymptomatic spread is difficult to trace without a comprehensive testing and sequencing surveillance program. It is entirely possible that further mutations in the S-protein may allow a new strain to develop which will require a new round of vaccine development and inoculation campaign. We are already seeing a significant number of verified reinfections so it is clear that naturally acquired immunity wanes in protectiveness over time, which is not unexpected.
In short, the USA is not “approaching herd immunity”; instead we are seeing a drop in infections and deaths because we are past the December holidays infection spike, and because many states as well as the current federal administration are applying and enforcing more rigorous masking and physical separation requirements. It is unlikely that we will achieve any herd immunity threshold without a comprehensive vaccination campaign, and even then we will probably see new variants and strains develop because of both resistance to vaccination and the ability of many mammals to host this virus and potentially facilitate spillback into the human population.
Well there’s a problem right there, because, after extensive contact tracing, it’s well known ‘in Australia’ that the ‘mean number of replications per infection’ is not a useful number, because the variance is so large. Most people infect nobody. A small number of people cause outbreaks. It’s ‘obvious to me’ that if the people who cause outbreaks all become immune, the disease will decrease to a background level.
Australia (where I live and which has had the contact tracing) has not had significant outbreaks of the new variants. My understanding is that most of the COVID in the USA is still ‘old variants’, so the present sharp decline reflects the behavior of ‘old variants’?
I have ‘no idea what herd immunity means’, so what I’m actually wondering is ‘this disease might just be becoming naturally endemic in the USA rather than epidemic’, not ‘some theoretical herd immunity threshold’.
The sharp decline in January USA cases indicates that you are past the November infection spike, and that December did not cause an infection spike. This seems to be in contradiction to the idea that there was poor compliance in December.
Anyway, I’m not asserting an opinion other than ‘dissatisfied with present knowledge’, so debate, education and alternative assertions are welcome.
It is certainly true that there is a skewness in the infection data, and that there are a relatively small minority fraction of infected people who are responsible for the majority of “superspreader” events where dozens or hundreds of people are infected; however, from what I’ve seen there is no good trending in the data to allow for predicting specific groups or individuals who are prone to this, and it isn’t clear how much of this is innate versus behavioral. At this point, I think we have to assume that individuals who are prone to much higher rates of transmitting the disease to others are more or less evenly distributed in the population such that inoculating a representative demographic cross section would still result in the same general replication number among uninoculated populations.
In the US, we really have no idea just how widespread new variants are. The lack of genomic testing and surveillance is a stunning failure to take action to try to prevent wider contagion, with at least a few state health officials expressing the obtuse opinion that it didn’t matter which variant was dominant. Even with health departments stretched and labs worked to capacity, it would make sense to at least do enough sample testing of infectious people to get a statistically meaningful estimate, and we do not have that in any state to any degree of statistical confidence.
I have to disagree with that assessment. We see cases starting to rise in early December, which correlates with November (American Thanksgiving holiday, 26 November), and then at least a local peak in reported infections in early-to-mid-January for most states, which corresponds with Christmas-time gatherings, with a falloff in new cases after that as people stopped holiday gatherings and some states got more serious about imposing restrictions. There are a few states that buck this trend but they tend to be rural states with lower population densities and also lower per capita rates of testing. There may have been better compliance in December indicated by the lower peaking in January than in December, but the trend of local peaking is still there.
Regardless, at this point there is no reason to believe that we will assuredly achieve a herd immunity threshold without vaccination; aside from the native infectiousness of this pathogen, it is clear that at least in some significant percentage of people immune response wanes in a few months after exposure, which is consistent with what is known about other common human-infecting coronaviruses. With an effective vaccine and a vigorous inoculation campaign it should be possible to push this contagion down below the epidemic threshold and make it no more of a threat than influenza or any other of a number of infectious pathogens (provided, of course, that it doesn’t mutate into a really aggressive strain that evades the current crop of vaccines entirely, and even then, it is probably possible to make a vaccine that targets other parts of the capsid that are not as prone to mutation as the S-protein) but it does not appear that we would be able to get there via naturally acquired immunity through infection.
I don’t think it does considering a huge percentage of people who were not compliant in avoiding large gatherings at Thanksgiving are the same people who weren’t compliant about the same in December. If they got sick and/or spread covid at Thanksgiving, they weren’t also going to get sick again at Christmas/New Years.
??? In the US, cases started to rise very slightly in September, noticeably in October, and dramatically throughout November. The biggest increases took place before Thanksgiving, not after.
I think you’re placing too much importance on the current downward trend. As several people have pointed out it’s a combination of the natural progression of the disease and human attempts at mitigation. It does not signal a significant change in how the virus spreads or how we should respond to it.
Do you know this for a fact, or is it an assumption? I wouldn’t assume it.
First, not all people celebrate major holidays at both times. People who are not Americans, but foreigners living here often don’t celebrate Thanksgiving unless they are invited somewhere, and it’s doubtful they were this last year. Then, lots of people don’t celebrate a major holiday in December. Chanukah, for example, is not such a big deal that most Jews I know feel a pressing need to be with family.
Second, a lot of people were really starved to be with family, and gathered for Thanksgiving, but then, having satisfied the need, listened to cautions in December, and contrariwise, people who resisted in November were even more anxious to see family a month later. I actually know of people who said they were so “good” in November, staying away, that they really “deserved” to see family by December. Seriously.
Is it, ‘certainly true’? I’m going to hold you to task here, because I’m not aware of any firm evidence of this, despite its widespread belief. Which events do you have in mind, where hundreds of people were infected? (And can you think of any other explanations for what was observed, in those cases?) You talk about surveillance in your post, and despite the US not having the most rigorous data sets from it, there has been plenty of it worldwide. How ubiquitous is this pattern of one person infecting ‘dozens or hundreds’?
My impression is that the contact tracing that’s been done, particularly in places that can do it with genomic sequencing (and thus, at least theoretically, demonstrate something beyond coincidence), points to the vast, vast preponderance of spread coming in other ways.
So, can you provide cites that demonstrate the ‘certainty’ of that purported ‘truth’?
This paragraph is chock full of assumptions and estimates (at least one not expressly described as such), and of course is based on theoretical models (which is not made expressly clear). You are aware of competing models, I would assume? And ones that do better with observed infection data, at that. The simple threshold model you seem to be using here (some might recognize it as similar to something you might see in middle-school algebra) assumes homogenous populations, no? And the real world is far from that?
Do you think there were many people who got together on Thanksgiving and, no one having gotten sick as a result, figured they could safely get away with it again a month later?
I’m trying to parse what is actually being asked here. To the plain meaning, do I think many people got lucky and didn’t get sick in November, and decided to try again in December, my answer is a plain “No.”
First, I think a lot of people who otherwise would have traveled, in fact did not, and second, I think a pretty good portion of the people who did travel did not get lucky-- at least someone at their gathering became sick within two weeks, and that probably gave a scare to everyone.
But mostly, I’m wiggling around the word “many.” For many people to get lucky, many people had to defy the CDC strong suggestion not to travel. I think a lot of people didn’t travel. Enough did to cause alarm though, and enough of them got sick to be a problem.
There’s a contradiction: first, it’s being claimed that the people who went ahead and traveled in November and December caused a spike in infections, then it’s being claimed that “many” of those who traveled did not get sick.
I understand how both those things could be true-- it doesn’t take a lot of people getting infected to cause a problem with shortages of hospital space, and soforth, but if that’s the case, then it’s not necessary to conjure up a lot of uninfected travelers. You can simply speculate that there were fewer travelers, but a higher percentage got infected. Either way, there are the same number of infections.
This is why I’d like to see actual stats on travelers to know for sure how many traveled both times, and how many each time were what percentage of the population.
