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Fauci Flubs Herd Immunity

03 Sunday Jan 2021

Posted by pnoetx in Coronavirus, Herd Immunity, Public Health, Vaccinations

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Acquired Immunity, Anthony Fauci, Covid-19, Herd Immunity, Hererogeneity, HIT, Masks, Max Planck Institute, Measles, MMR Vaccine, R0, Reproduction Rate, T-Cells. Pre-Immunity, Tyler Cowen, Vaccinations. Fragile Immunity

Anthony Fauci has repeatedly increased his estimate of how much of the population must be vaccinated to achieve what he calls herd immunity, and he did it again in late December. This series of changes, and other mixed messages he’s delivered in the past, reveal Fauci to be a “public servant” who feels no obligation to level with the public. Instead, he crafts messages based on what he believes the public will accept, or on his sense of how the public must be manipulated. For example, by his own admission, his estimates of herd immunity have been sensitive to polling data! He reasoned that if more people reported a willingness to take a vaccine, he’d have flexibility to increase his “public” estimate of the percentage that must be vaccinated for herd immunity. Even worse, Fauci appears to lack a solid understanding of the very concept of herd immunity.

Manipulation

There is so much wrong with his reasoning on this point that it’s hard to know where to start. In the first place, why in the world would anyone think that if more people willingly vaccinate it would imply that even more must vaccinate? And if he felt that way all along it demonstrates an earlier willingness to be dishonest with the public. Of course, there was nothing scientific about it: the series of estimates was purely manipulative. It’s almost painful to consider the sort of public servant who’d engage in such mental machinations.

Immunity Is Multi-Faceted

Second, Fauci seemingly wants to convince us that herd immunity is solely dependent on vaccination. Far from it, and I’m sure he knows that, so perhaps this too was manipulative. Fauci intimates that COVID herd immunity must look something like herd immunity to the measles, which is laughable. Measles is a viral infection primarily in children, among whom there is little if any pre-immunity. The measles vaccine (MMR) is administered to young children along with occasional boosters for some individuals. Believe it or not, Fauci claims that he rationalized a requirement of 85% vaccination for COVID by discounting a 90% requirement for the measles! Really???

In fact, there is substantial acquired pre-immunity to COVID. A meaningful share of the population has long-memory, cross-reactive T-cells from earlier exposure to coronaviruses such as the common cold. Estimates range from 10% to as much as 50%. So if we stick with Fauci’s 85% herd immunity “guesstimate”, 25% pre-immunity implies that vaccinating only 60% of the population would get us to Fauci’s herd immunity goal. (Two qualifications: 1) the vaccines aren’t 100% effective, so it would take more than 60% vaccinated to offset the failure rate; 2) the pre-immune might not be identifiable at low cost, so there might be significant overlap between the pre-immune and those vaccinated.)

Conceptual Confusion

Vaccinations approaching 85% would be an extremely ambitious goal, especially if it is recommended annually or semi-annually. It would be virtually impossible without coercion. While more than 91% of children are vaccinated for measles in the U.S., it is not annual. Thus, measles does not offer an appropriate model for thinking about herd immunity to COVID. Less than half of adults get a flu shot each year, and somewhat more children.

Fauci’s reference to 85% – 90% total immunity is different from the concept of the herd immunity threshold (HIT) in standard epidemiological models. The HIT, often placed in the range of 60% – 70%, is the point at which new infections begin to decline. More infections occur above the HIT but at a diminishing rate. In the end, the total share of individuals who become immune due to exposure, pre-immunity or vaccination will be greater than the HIT. The point is, however, that reaching the HIT is a sufficient condition for cases to taper and an end to a contagion. If we use 65% as the HIT and pre-immunity of 25%, only 40% must be vaccinated to reach the HIT.

Heterogeneity

A recent innovation in epidemiological models is the recognition that there are tremendous differences between individuals in terms of transmissibility, pre-immunity, and other factors that influence the spread of a particular virus, including social and business arrangements. This kind of heterogeneity tends to reduce the effective HIT. We’ve already discussed the effect of pre-immunity. Suppose that certain individuals are much more likely to transmit the virus than others, like so-called super-spreaders. They spur the initial exponential growth of a contagion, but there are only so many of them. Once infected, no one else among the still-susceptible can spread the virus with the same force.

Researchers at the Max Planck Institute (and a number of others) have gauged the effect of introducing heterogeneity to standard epidemiological models. It is dramatic, as the following chart shows. The curves simulate a pandemic under different assumptions about the degree of heterogeneity. The peak of these curves correspond to the HIT under each assumption (R0 refers to the initial reproduction number from infected individuals to others).

Moderate heterogeneity implies a HIT of only 37%. Given pre-immunity of 25%, only an additional 12% of the population would have to be infected or vaccinated to prevent a contagion from gaining a foothold for the initial exponential stage of growth. Fauci’s herd immunity figure obviously fails to consider the effect of heterogeneity.

How Close To the HIT?

We’re not as far from HITs as Fauci might think, and a vaccination goal of 85% is absurd and unnecessary. The seasonal COVID waves we’ve experienced thus far have faded over a period of 10-12 weeks. Estimates of seroprevalence in many localities reached a range of 15% – 25% after those episodes, which probably includes some share of those with pre-immunity. To reach the likely range of a HIT, either some additional pre-immunity must have existed or the degree of heterogeneity must have been large in these populations.

But if that’s true, why did secondary waves occur in the fall? There are a few possibilities. Of course, some areas like the upper Midwest did not experience the springtime wave. But in areas that suffered a recurrance, perhaps the antibodies acquired from infections did not remain active for as long as six months. However, other immune cells have longer memories, and re-infections have been fairly rare. Another possibility is that those having some level of pre-immunity were still able to pass live virus along to new hosts. But this vector of transmission would probably have been quite limited. Pre-immunity almost surely varies from region to region, so some areas were not as firmly above their HITs as others. It’s also possible that infections from super-spreaders were concentrated within subsets of the population even within a given region, in certain neighborhoods or among some, but not all, social or business circles. Therefore, some subsets or “sub-herds” achieved a HIT in the first wave, but it was unnecessary for other groups. In other words, sub-herds spared in the first wave might have suffered a contagion in a subsequent wave. And again, reinfections seem to have been rare. Finally, there is the possibility of a reset in the HIT in the presence of a new, more transmissible variant of the virus, as has become prevalent in the UK, but that was not the case in the fall.

Fragility

Tyler Cowen has mentioned another possible explanation: so-called “fragile” herd immunity. The idea is that any particular HIT is dependent on the structure of social relations. When social distancing is widely practiced, for example, the HIT will be lower. But if, after a contagion recedes, social distancing is relaxed, it’s possible that the HIT will take a higher value at the onset of the next seasonal wave. Perhaps this played a role in the resurgence in infections in the fall, but the HIT can be reduced via voluntary distancing. Eventually, acquired immunity and vaccinations will achieve a HIT under which distancing should be unnecessary, and heterogeneity suggests that shouldn’t be far out of reach.

Conclusion

Anthony Fauci has too often changed his public pronouncements on critical issues related to management of the COVID pandemic. Last February he said cruises were fine for the healthy and that most people should live their lives normally. Oops! Then came his opinion on the limited effectiveness of masks, then a shift to their necessity. His first position on masks has been called a “noble lie” intended to preserve supplies for health care workers. However, Fauci was probably repeating the standing consensus at that point (and still the truth) that masks are of limited value in containing airborne pathogens.

This time, Fauci admitted to changing his estimate of “herd immunity” in response to public opinion, a pathetic approach to matters of public health. What he called herd immunity was really an opinion about adequate levels of vaccination. Furthermore, he neglected to consider other forms of immunity: pre-existing and already acquired. He did not distinguish between total immunity and the herd immunity threshold that should guide any discussion of pandemic management. He also neglected the significant advances in epidemiological modeling that recognize the reality of heterogeneity in reducing the herd immunity threshold. The upshot is that far fewer vaccinations are needed to contain future waves of the pandemic than Fauci suggests.

Statists Might Like To Vaccinate Against Many Things

25 Monday Nov 2019

Posted by pnoetx in Vaccinations

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Anti-Vaxxers, Community Protection Threshold, Contagion, Contra-Indications, Externality, Federaalism, Herd Immunity, Immunization, Jeffrey Singer, Lancet, Measles, Mercury, Michigan Vaccine Law, Post Hoc Ergo Propter Hoc, Precautionary Principle, Price Discrimination, Private Governance, Vaccine Hesitancy, Vaccine Preservatives, Vaccine Resistors, Whooping Cough

The vaccine debate illustrates a widespread misunderstanding about the meaning of an “advanced society”. It does not mean that difficult social problems must be dealt with always and everywhere in a uniform way, as supporters of vaccine mandates seem to assume. Instead, it often means that society can respect differences in the preferences of individuals by allowing varied approaches to problem-solving across jurisdictions, as well as across public and private institutions. This latter notion of advancement respects individual freedom and facilitates experiential social learning. But is that varied approach wise in a world of communicable diseases?

One standard of “community” protection assumes that vaccines work with a high degree of certainty within groups of individuals, especially with a second booster. The share of the population vaccinated against most common childhood diseases is fairly high. In fact, these shares mostly exceed their respective “community protection thresholds” — the percentage required to prevent a particular disease from spreading. That means achieving so-called “herd immunity”. Of course, that will not be true across many local subgroups. Nevertheless, if one accepts this standard, a runaway contagion in the U.S. is an extremely remote possibility, affording some flexibility for respecting preferences for and against vaccination.

My Friend, the Vaccine Resistor

One of my best friends is a passionate vaccine resistor (VR). I won’t say he’s “vaccine hesitant” because that doesn’t come close to his position. I won’t call him an “anti-vaxxer” because he doesn’t mind if others avail themselves of vaccines (and besides, the term has taken on such derogatory connotation. He’s a fine fellow, very smart, lots of fun to be with, and we have plenty of mutual interests. We’ve argued about vaccinations before, and a few other medical and nutritional issues, but we mostly stay out of each others’ ways on these topics.

But I recently witnessed my pal get into a “debate” on social media with a mutual acquaintance and some of her connections. She happens to be a nurse. She’d posted a photo of an attractive young woman in a t-shirt imprinted, “Vaccines Cause Adults”. My buddy spoke up and said “Not for everyone!’, and he posted a link to an article that he felt supported his position. Of course, a number of barbed responses came his way. Okay, some of those were fair debate points, though barbed, but others were quite derisive, ad hominem attacks on him. He responded by posting links to more articles and research, which might not have been productive. It’s usually a waste of time to argue with people on social media. But to his great credit he maintained his equanimity. The episode made me feel a bit sad. People can be such assholes on social media. I was put off by the nurse’s refusal to moderate . That’s a typical pattern: posters allow their other friends to hurl terrible insults at anyone who disagrees, even when it’s an old friend. Mind you, I stayed on the sidelines in this case, except that I originally “liked” the nurse’s meme.

Later, I had a private exchange with my friend. I’m on board with vaccinations. I believe that widespread immunization contributes to public health, but I told him there are certain points on which I can sympathize with VRs. Without knowing the details, he encouraged me to write a blog post on the subject. I’m not sure he’ll like the results. However, as noted above, I’m willing to make a few concessions to my buddy’s side of the argument, and I wish we could identify a path that would settle the debate.

My Standpoint

This is one part my pal won’t like. Are VRs anti-science? First, VR’s come in several varieties. Some might resist only some vaccines and not others. But VRs do not disavow empiricism, as they claim their own set of empirical findings to support their position, however one might regard the research quality. 

I believe many VRs are misled by a serious post hoc ergo propter hoc fallacy: after this, therefore because of this. For example, for many observers, the purported link between autism and the measles, mumps and rubella vaccine was put to rest when the British medical journal Lancet retracted the original article supporting that claim as faulty. That doesn’t wash with more radical VRs, many of whom seem to have someone on the autism spectrum in their own families. They are understandably sensitive, but please forgive me: that suggests a need to find some external explanation, a source of blame not related to genetics.

Radical VRs are selective proponents of the precautionary principle: any risk of harm from a vaccine delivered in any amount is too great a risk. They seem reluctant to acknowledge the reality of a dose-response relationship, which bears on the risks of exposure to certain compounds often present in vaccine formulations. VRs will not acknowledge that vaccines present a manageable risk. And then there are the misleading references to disease incidence counts, as opposed to disease incidence rates, that are all too common (though my friend is almost certainly innocent on this count).

Vaccine resistance is not a new phenomenon, as the cartoon above from 1802 illustrates. Certain people will always find the idea of injecting germs into their systems deeply unsettling. Of course, that’s a very natural basis of resistance. A person’s body is their own property, after all. My default position is that an individual’s control over their own body is inviolable, and parents should always be the first authority over decisions about their children. The real issue, however, is the question of whether unvaccinated children inflict external costs on others.

Points of Contention

The major objections of VRs fall into several categories: 1) preservatives; 2) multiple viruses; 3) vulnerable infants; 4) contra-indications; 5) inefficacy; and 6) free choice. There may be others, but I’ll go with those.

Preservatives: Some vaccines still use a form of mercury, but a much more innocuous variant than the one VRs found so objectionable a few decades ago. Still, they object. And they object to many other compounds used in minute quantities as preservatives, such as formaldehyde, which occurs naturally in our bodies. I think the following test is helpful: if it were proposed that VRs take new versions of the vaccines that had zero preservatives, many would still refuse, especially if they were asked to pay the additional cost of providing them in that form. Thus, preservatives are revealed to be something of a side show.

Multiple Viruses: VRs object to the administration of vaccines that inoculate against several viruses in one dose or within a short window of time. This objection has some plausibility, since an injection of several different “bugs’ at once might place excessive stress on the body, even if the risk is still small. But again, would VRs volunteer to take single strain vaccines in a schedule over a lengthier period of time? Probably not.

Vulnerable Infants: VRs say it’s too risky to vaccinate infants in their first few months of life. This too is a plausible objection, and it would seem like a relatively easy concession to make in the interests of compromise … except, it won’t ever be good enough. Radical VRs will not agree to having their children vaccinated at any age.

Contra-Indications: There are undoubtedly genetic factors that pre-dispose certain individuals to an adverse reaction to certain vaccines. These might be rare, so an effort to compromise by requiring a thorough genetic profile before vaccination would be costly. I believe profiling is a reasonable demand for individuals to make, however, provided they pay the cost themselves.

Inefficacy: My friend posted an intriguing article about the drastic declines that occurred in the incidence of various diseases before the introduction of vaccines to prevent those diseases. This might not be the same link, but it makes the same argument. That doesn’t mean vaccines don’t work, of course. There is a vast literature that shows that they do. Bing it! And in cases such as smallpox, the use of “folk applications” of puss to a small scratch in the skin were in use long before the vaccine was available. Nevertheless, the VRs contend that the historical rates of disease incidence provide evidence against vaccinating. They also contend that diseases like measles are not serious enough to warrant precautions like vaccines. Measles can be deadly, though not as deadly as the flu.

Free Choice: This is the point on which I’m most sympathetic to VRs. Again, we own our own bodies and should have authority over our own minor children, yet communicable diseases seem to be a classic case of externality. Susceptible individuals may inflict a cost on others by refusing vaccination or segregation. Other people own their bodies too, and they have a right to avoid exposure. They too can isolate themselves or take precautions as they deem necessary. If both parties wish to participate in society, then both hold rights they allege to be threatened by the other. That complicates the task of reconciling these interests in private, voluntary ways, and yet they often are reconciled privately.

Solutions?

The debate today often revolves around mandatory vaccination, which would be an extreme measure relying on the coercive power of the state. The rationale is that even a vaccinated majority would be subject to an unnecessarily high risk of infection when in frequent contact with an unvaccinated minority. It’s difficult to endorse such broad intrusiveness when we’re dealing with a negative externality of such minute probability. And such a policy is not at all defensible without exceptions for individuals for whom a vaccine is contra-indicated.

Tolerating differences in vaccination rules across cities, school districts, or even states, may be a reasonable approach to settling the debate in the long run. These variations allow empirical evidence to accumulate on the efficacy of different vaccine regimes. It also allows individuals and families to “vote with their feet”, migrating to jurisdictions that best suit their preferences. These are the basic foundations of federalism, a principle of great usefulness in preserving freedoms while addressing regional differences of opinion on contentious issues.

Michigan has a policy allowing unvaccinated children to attend schools, but a waiver must be obtained requiring the child’s parents to attend a vaccine education program. The policy is credited with increasing vaccination rates. The problem is that VRs tend to view this requirement as an infringement on their rights. Advocates of the policy might argue that the situation should be viewed as an arms-length, voluntary exchange between two parties, in this case a family and a public entity. The vaccine education program is just the price one must pay in lieu of vaccination. The exchange is not arms length, however, as it would be if the school were a private entity. The VR parents who refuse the waiver are not rebated for taxes paid for local schools. In fact, like all taxes, the payment is coerced.

It’s not always necessary to appeal to some form of government action, even at local levels. For example, private schools may require vaccination among enrollees, and private businesses, especially health care providers, may require staff to be vaccinated. Life and health insurers may wish to price risk differently for the unvaccinated. VRs might object that they are subject to discrimination by institutions requiring immunization, or who price discriminate in favor of the immunized, but VRs are free to form competitive institutions, even on small scales or as mutual companies. To the extent that such private rules are unjustified, the institutions who discriminate are likely to learn or lose eventually. That’s the beauty of market solutions. In these ways, non-coercive private governance is far preferable to action by the state.

Dr. Jeffrey Singer is an advocate of immunization who opposes mandatory vaccine laws, as he explained a few years ago in “Vaccination and Free Will“. He suggested elsewhere, in “Seeking Balance In Vaccination Laws“, that schools, instead of requiring immunization, could mitigate the risk of a contagion by insisting that unvaccinated children be held out of school when a particular threat arises and remain out until it passed. That’s a reasonable idea, but I suspect many pro-vax parents would fear that it doesn’t go far enough in protecting against the introduction of a disease by an unvaccinated child.

Conclusion

Recent increases in the incidence of diseases such as measles, mumps and whooping cough are extremely troubling. Whether these outbreaks bear any relationship to patterns of vaccination in the population is certainly a valid question. To the extent that more families and individuals wish to be immunized, and that private institutions wish to take action to increase vaccination rates within their sphere of influence, I’m all for it. Vaccination laws are a different matter.

Political action at the local level might mean that school districts and other public entities will require vaccinations or vaccine education programs. Alternatives exist for those refusing to vaccinate, but broad mandatory vaccination is too coercive. Such measures carry significant costs, not least of which is a loss of liberty and normalization of losses of liberty. It’s not clear that a vaccination mandate at the national level, or even a state vaccination mandate, can offer benefits sufficient to justify those costs. Nudges are irritating and may be costly, but forcible intrusions are way out-of-bounds. Unfortunately, there are parties that simply can’t resist the temptations of behavioral control, and that’s worthy of resistance. Let’s continue to muddle through with an essentially federalist approach to vaccination policy. I regard that as a hallmark of an advanced society.

 

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