Vaccination and the Transmission of COVID-19 [COVID-19, sci/bio/med, Patreon]

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You may have noticed some very mixed messages about the COVID-19 vaccines. On one hand, the message that even if you're vaccinated, you can still transmit COVID-19. On the other hand, the message that it's crucial for everyone to get vaccinated as soon as possible, so we can attain herd immunity.

This raises the obvious question: how can something that doesn't stop you from transmitting a virus bring about herd immunity? Herd immunity is premised on stopping transmission, right? So which is it: does vaccination prevent transmission or not? Are we working towards herd immunity or not?

And why is the messaging so mixed?

The answers turn out the be interesting, and very, very exciting.

1.

There are, for purposes of this conversation, two antibody responses our immune systems have to infection: making IgA and making IgG.

[...] natural infection induces both mucosal antibody responses (secretory immunoglobulin A (IgA)) and systemic antibody responses (IgG). The upper respiratory tract is thought to be mainly protected by secretory IgA, whereas the lower respiratory tract is thought to be mainly protected by IgG.

This explanation is from Florian Krammer's Sept 23, 2020 Nature article, "SARS-CoV-2 vaccines in development".

This distinction is hugely important, because, for one thing, by "lower respiratory tract", he means lungs. Lungs are protected by IgG.

What that means is that if your body learns to make IgG to fight off an infection, that infection can't take hold in your lungs. Once your IgG antibodies have learned to recognize a pathogen, your lungs are protected from it.

The other reason it's important is

Vaccines that are administered intramuscularly or intradermally induce mainly IgG, and no secretory IgA.

Intramuscularly. You know. Like a shot in the arm.

All injected vaccinations – all – apparently target the IgG immune response. We don't know of any vaccine that provokes the body to make IgA.

You perhaps can see where this is going. The COVID-19 vaccines, like every other vaccination you have gotten in your life, provoke a robust IgG response. They teach your body to make anti-SARS-CoV-2 IgG antibodies, which will attack any SARS-CoV-2 that gets into your lungs.

It does not, however, do anything to provoke an IgA response, to defend your nose, sinuses, and throat. There was never any reason to think it would, being as it was a intramuscular inoculation, and intramuscular inoculations having never provoked an IgA response before, nobody was expecting it now.

The basic assumption of all the vaccines under development, as that article explains, was that they'd protect the lungs – and most of the rest of the body – but wouldn't protect the upper respiratory system.

The way COVID-19 kills is, overwhelmingly, by Acute Respiratory Distress Syndrome: an attack on the lungs. If SARS-CoV-2 can't get a toe-hold in your lungs, it can't kill you. It can't even hurt you very much.

This is why you keep hearing how the vaccines are almost proof against "severe COVID-19", and prevent hospitalization and death from COVID-19.

But it's also why you keep hearing that people might still be able to transmit COVID-19, even if vaccinated.

Because the concomitant of vaccination not provoking IgA response, and IgA response being the one we think is what protects the nose and rest of the upper windway, is that vaccination would leave your upper respiratory system defenseless against COVID-19.

Based on this, logically it follows that vaccinated, you can still catch COVID-19 – but only in your upper respiratory system.

Put another way, it is a reasonable surmise that what the vaccines do for us is turn COVID-19 from a fatal pulmonary/vascular illness to a simple head cold.

And that, dare I say it, is nothing to sneeze at.

But there's more.

2.

Here's something I've seen almost nowhere discussed. If what I've written above is correct, and even if there's nothing more to it (spoiler: there is), then what the COVID-19 vaccines do for us is flatten the curve.

You remember "flatten the curve", right? The basic premise is that by reducing the number of people with hospitalizing severe cases of COVID-19 simultaneously – even if that number of people have to go through severe COVID-19 eventually – we prevent the health care system from getting crushed under the influx of dying patients. Like what happened in Wuhan, Italy, and NYC, and is happening in India right now. Patients who do get severe COVID-19 – and anything else they might need care in a hospital for – have much, much better chance of survival if there are beds in the hospitals for them, and people aren't fighting each other for oxygen canisters in the hospital parking lots.

Widespread vaccination with a vaccine which mostly prevents severe COVID-19 means that those people who can't get the vaccine, or for whom, for some idiosyncratic biological reason, the vaccine doesn't work to protect them, if they do get COVID-19, there will be an abundance of hospital beds, PPE, oxygen, ventilators, ECMO machines, pulmonologists, ICU nurses, etc, to get them through.

3.

For just this reason alone, the relaxing of mask rules make more sense. The purpose of trying to prevent the spread of COVID-19 was two-fold: 1) to prevent injury and death, and 2) to prevent the collapse of the healthcare system. Since the vaccines do an apparently excellent job at the former, and thus may be assumed to be likely proof against the latter, there's no more reason to try to prevent COVID-19 from spreading once the population is vaccinated.

There comes a point where from a public health stand-point preventing the spread of COVID-19 is no longer important.

Arguably, that point is once everyone who wants the vaccine gets it.

Before researching this, I'd been thinking the moral urgency in getting vaccination was to reach community immunity. But now I realize there is probably a different aim in exhorting the general public to get vaccinated. It's to flatten the curve and to protect as many people are willing and able to be protected from death and disability.

When one assumes that we can't prevent transmission, but that we can prevent severity and mortality, then the moral calculus changes. This is no longer a group project the same way: we don't need everyone to get vaccinated, the way we would if pursuing herd immunity. The percent of the population needed to be vaccinated to flatten the curve is much smaller than the percent needed to reach herd immunity.

If we've given up hope of preventing transmission – if transmission is going to happen regardless of the vaccine – then, to a first approximation, vaccination is a personal choice. Just so long as enough people to flatten the curve choose it, after that, the rest of us don't need the remainder to get vaccinated.

If, say, a third (I pulled that number out of the air) the US population decides they don't want that protection? Okay, enjoy your ARDS roulette.

This puts the CDC's recent decision to relax recommendations on masking and so forth in a different light. If their aim is to flatten the curve, they just need to get enough shots into enough arms to do that. Arguably, they have a responsibility to wait until enough vulnerable people are able to get their shots before dropping all protections.

But after that point, whether or not someone lets COVID-19 be a deadly threat to them is on their own head. If you choose not to get the vaccination that will prevent COVID-19 from killing you if you get it, so be it. Why should the state protect you from yourself? Why should the rest of us?

There's an old story (which has both been debunked, and de-debunked) about how when the lightning rod was invented, religious authorities denounced it as violating God's will by protecting buildings from His holy wrath. The story has it that, consequently, for a while there, the tall buildings under secular authorities all got lightning rods, and the only buildings being smote by the Lord and burnt to the ground were churches.

Whether or not that was actually true about lightning rods and churches, I expect we may be entering a period of the pandemic in the US where it proves true of vaccination and covidiots.

I suspect this is one of the things the behavior of the CDC and Fauci and by implication the Biden administration indicates they're thinking.

But note the hypothetical: that's if vaccination has no effect on transmission. And there's more to the story.

4.

We can make a distinction between catching the virus and catching the disease. It would be best of all if you couldn't catch the virus at all, but if you have to still be able to be infected by SARS-CoV-2, it would be better if you didn't come down with full-blown COVID-19 when you did. In this sense, the aim of the vaccines is to make us resistant to the disease, not the virus.

But it sure would be nice if we were also entirely resistant to the virus: then we wouldn't be able to become infected with SARS-CoV-2 at all, wouldn't even get COVID-19 as a head cold, and wouldn't be able to pass it on.

This kind of total resistance is called "sterilizing immunity". When you have sterilizing immunity to a pathogen, one's body is like poison to the pathogen, killing it off.

You may have seen in the news or in science explainers this term, "sterilizing immunity", and the question of whether or not the COVID vaccines cause sterilizing immunity.

The present understanding is that to have sterilizing immunity, you need antibodies in your mucus, and the mucus antibodies are IgA, and we don't get IgA antibodies from intramuscular vaccination, and the COVID vaccinations are intramuscular. So just from that chain of reasoning, nobody much expects sterilizing immunity from the COVID vaccinations.

Except....

The way one gets IgA antibodies – for sterilizing immunity – is by natural infection. You know, by getting the infection on your mucus membranes and your body learning to make IgA in response. That includes infection by SARS-CoV-2: 2021 Jan 20: Sci Transl Med: "IgA dominates the early neutralizing antibody response to SARS-CoV-2 ".

So I wonder if intramuscular vaccination against COVID-19 is an indirect path to herd immunity, even if vaccination did nothing to reduce transmission. If COVID continues to transmit, and is going to circulate in the population of vaccinated people as a benign head cold, then eventually all the vaccinated people will wind up with IgA responses organically, bringing about sterilizing immunity in the end.

But that's if vaccination doesn't reduce transmission.

5.

When the vaccines were approved and initially administered to the public, the understanding was we weren't going to get sterilizing immunity out of them, because they were intramuscular, and would only provoke IgG responses.

The circumspect position was to anticipate that all the COVID vaccines would do for us, societally, is make people resistant to being killed or permanently injured by COVID-19, and that it wouldn't stop transmission.

And that all makes logical sense for the above reasons.

Except....

We regularly rely on vaccines – measles, mumps, rubella; HPV; chickenpox; etc – that are intramuscular to stop transmission and cause herd immunity.

2021 Jan 28: Scientific American: "Vaccines Need Not Completely Stop COVID Transmission to Curb the Pandemic by Stacey McKenna:

Although many vaccines widely used today (against measles, for example) produce very effective sterilizing immunity, others, such as the hepatitis B vaccine, do not. With these vaccines, an individual’s immune system is trained to prevent illness, yet the pathogen can persist in that person’s body, potentially allowing them to infect others. A lack of sterilizing immunity means that the pathogen can continue to circulate in a population, where it may cause illness in unvaccinated and vulnerable people or evolve to evade our immune responses, [Dawn] Bowdish [a professor of pathology and molecular medicine at McMaster University] explains.

Sterilizing immunity may have been a lofty goal for COVID-19 vaccine manufacturers, though not necessary to curb disease. According to [Natasha] Crowcroft, [senior technical adviser for measles and rubella at the World Health Organization,] the very concept of such immunity is nuanced. “In reality, the spectrum of protection might best be framed as the extent to which vaccination prevents transmission of the wild-type virus or bacteria,” she says.

And how can it do that? Why, the dose-response relationship (previously):

The case of rotavirus—which causes severe vomiting and watery diarrhea and is especially dangerous to infants and young children—is fairly straightforward. Vaccination limits, but does not stop, the pathogen from replicating. As such, it does not protect against mild disease. By reducing an infected person’s viral load, however, it decreases transmission, providing substantial indirect protection. According to the Centers for Disease Control, four to 10 years after the 2006 introduction of a rotavirus vaccine in the U.S., the number of positive tests for the disease fell by as much as 74 to 90 percent.

Stands to reason: if your body harbors less virus, you have less virus to share with your neighbors; if you have fewer symptoms that result in expelling virus laden particles of bodily fluids, you will share what virus you have less than you would if you were sneezing, coughing, or puking.

The pathway to vaccine-mediated control of an infectious disease is not always so direct. Ultimately, whether, and to what degree, inoculation prevents transmission depends on the pathogen itself, the host or hosts it infects and the interaction between the two, Bowdish says.

For example, vaccines against Bordetella pertussis, the primary bacterium that causes whooping cough, or pertussis, do a great job of preventing illness but do not entirely clear the pathogen. [discussion of B. pertussis infection elided] Nevertheless, the introduction of pertussis vaccines in the 1940s cut annual U.S. cases from more than 100,000 to fewer than 10,000 by 1965. [...]

Influenza may provide the best blueprint of what to expect going forward. The most common flu vaccine—the inactivated virus—is not “truly sterilizing because it doesn’t generate local immune response in the respiratory tract,” Crowcroft says. This fact, coupled with low immunization rates (often shy of 50 percent among adults) and the influenza virus’s ability to infect and move between multiple species, enables it to constantly change in ways that make it hard for our immune system to recognize. Still, depending on the year, flu vaccines have been shown to reduce hospitalizations among older adults by an estimated 40 percent and intensive care admissions of all adults by as much as 82 percent.

[...] ample precedent points to vaccines driving successful containment of infectious diseases even when they do not provide perfectly sterilizing immunity. “Measles, diphtheria, pertussis, polio, hepatitis B—these are all epidemic-prone diseases,” Crowcroft says. “They show that we don’t need 100 percent effectiveness at reducing transmission, or 100 percent coverage or 100 percent effectiveness against disease to triumph over infectious diseases.”

6.

This, it seems to me, is where another of the mixed messages come from. On the face of it, based on what we know about intramuscular vaccines in general, it doesn't seem likely that an intramuscular COVID vaccine would give us sterilizing immunity, but that doesn't mean it won't impact transmission. It might not eliminate it, but it might reduce it. Other vaccines radically reduce transmission of their target diseases without being sterilizing.

So I think nobody wanted to come out and say "Well, other vaccines sometimes, kind of randomly, turn out to impact transmissibility rather a lot" when all we knew for certain is intramuscular means no sterilizing immunity. And I think governmental authorities, in particular, were not at all keen to get anybody's hopes up, when at the time, nobody had any idea what the effect on transmissibility would wind up being for the COVID vaccines.

But that was then. Then this came out:

2021 Feb 8: MedRXiv.org (preprint): "Decreased SARS-CoV-2 viral load following vaccination" [PFD] by Livein-Tiefenbrun, et al.:

Beyond their substantial protection of individual vaccinees, it is hoped that the COVID-19 vaccines would reduce viral load in breakthrough infections thereby further suppress onward transmission. Here, analyzing positive SARS-CoV-2 test results following inoculation with the BNT162b2 [Pfizer-BioNTech] mRNA vaccine, we find that the viral load is reduced 4-fold for infections occurring 12-28 days after the first dose of vaccine. These reduced viral loads hint to lower infectiousness, further contributing to vaccine impact on virus spread.

There is it, a mechanism by which at least the Pfizer-BioNTech vaccine might reduce transmission.

It wasn't proof that a vaccine did reduce transmission. It was, as the authors said, a "hint" that it could happen. It was plausible to wonder if the observed lower viral loads would translate, in practice, to vaccination lowering rates of transmission.

But the only way to know how COVID vaccines affect transmissibility is to give the vaccine to a whole lot of people and wait and see how they transmit COVID.

Which we have now done.

7.

2021 April 28: BBC: "Covid: One dose of vaccine halves transmission - study":

A single dose of a coronavirus vaccine can reduce household transmission of the virus by up to half, a study shows.

Those given a first dose of either the Pfizer or AstraZeneca vaccines - and who became infected three weeks later - were between 38% and 49% less likely to pass the virus on than unvaccinated people, [Public Health England] found.

[...]

The study, which has yet to be fully peer-reviewed, included more than 57,000 contacts from 24,000 households in which there was a lab-confirmed coronavirus case that had received a vaccination, compared with nearly one million contacts of unvaccinated cases.

It was a bit hard to scare up the original source for this, because it was apparently announced in, but not published in, the BMJ:

2021 Apr 28: BMJ: "Covid-19: One dose of vaccine cuts risk of passing on infection by as much as 50%, research shows" It has very little more information than appears in that BBC article based on it, but it does link to it:

2021 undated, file last modified Apr 28: Impact of vaccination on household transmission of SARS-COV-2 in England [PDF], Harris et al.

These results show that the likelihood of household transmission is 40-50% lower for households in which the index cases are vaccinated 21 days or more prior to testing positive (compared to no vaccination), with similar effects for both ChAdOx1 nCoV-19 [AstraZeneca] and BNT162b2 [Pfizer/BioNTech] vaccines. Results persisted after adjustment for measured covariates. This effect on onward transmission in the household was particularly apparent for index cases aged less than 70 years. A matched case-control analysis also demonstrated similarly reduced odds ratios for secondary infections in household contacts.

I have to say, this is one of the most difficult-to-read scientific articles I've ever tackled, not just because of the science, but because of the... casual... way it's presented. I suppose if you have findings like this, many sins are forgiven. I welcome critiques of its actual science.

From the BMJ news item:

Public Health England’s head of immunisation, Mary Ramsay, said, “Vaccines are vital in helping us return to a normal way of life. Not only do vaccines reduce the severity of illness and prevent hundreds of deaths every day, we now see they also have an additional impact on reducing the chance of passing covid-19 on to others. I encourage anyone who is offered a vaccine to take it as soon as possible.”

8.

2021 May 14 (updated May 15): NYTimes: "Why the C.D.C. Changed Its Advice on Masks" by Apoorva Mandavilli:

For months, federal officials have vigorously warned that wearing masks and social distancing were necessary to contain the pandemic. So what changed?

Introducing the new recommendations on Thursday, Dr. Rochelle P. Walensky, the C.D.C. director, cited two recent scientific findings as significant factors: Few vaccinated people become infected with the virus, and transmission seems rarer still; and the vaccines appear to be effective against all known variants of the coronavirus.

[...]

“The science is quite clear on this,” said Zoë McLaren, a health policy expert at the University of Maryland, Baltimore County. Mounting evidence indicates that people who are vaccinated are highly unlikely to catch or transmit the virus, she noted.

The risk “is definitely not zero, but it’s clear that it’s very low,” she said.

One of the lingering concerns among scientists had been that even a vaccinated person might carry the virus — perhaps briefly, without symptoms — and spread it to others. But C.D.C. research, including the new study, has consistently found few infections among those who received the Pfizer-BioNTech and Moderna vaccines.

“This study, added to the many studies that preceded it, was pivotal to C.D.C. changing its recommendations for those who are fully vaccinated against Covid-19,” Dr. Walensky said in a statement on Friday.

Other recent studies confirm that people who are infected after vaccination carry too little virus to infect others, said Florian Krammer, a virologist at the Icahn School of Medicine at Mount Sinai [and incidentally the author of the Nature piece, above].

“It’s really hard to even sequence the virus sometimes because there’s very little virus, and it’s there for a short period of time,” he said.

Now, I don't know what "the science" that is quite clear to which McLaren refers is, I do not know to what "mounting evidence" she refers, because the New York Fucking Times did not deign to tell us.

Nor do I know in what scientific literature repose those findings that changed Walensky's mind, because not only doesn't the NY Times say, I could find nothing to that account on all of CDC.org as of when last I checked mid-May.

In fact, the only thing I could find about the science of the effect of vaccination on the transmissibility of SARS-CoV-2 was dated 2021 Apr 2, "Science Brief: Background Rationale and Evidence for Public Health Recommendations for Fully Vaccinated People, which says merely,

A growing body of evidence suggests that fully vaccinated people are less likely to have asymptomatic infection and potentially less likely to transmit SARS-CoV-2 to others. However, further investigation is ongoing.

and it cited the Feb 8 Livein-Tiefenbrun viral load study, saying, "This observation may indicate reduced transmissibility, as viral load has been identified as a key driver of transmission."

So nothing here explicates what, exactly, the CDC found so convincing. Was it the Apr 28 PHE pre-print paper? Because "reduce by as much as half the risk" doesn't seem to be the same as "definitely not zero, but it’s clear that it’s very low". Do they have other pertinent studies in mind? I've looked, but haven't found anything. I gather there's a relevant study in the US under way, but it won't be done for months.

So I don't know if the CDC knows something I don't, or whether the CDC is making decisions for reasons other than the ones its telling us about.

I mean, maybe I'm right, above, in my hypothesis that the CDC – and perhaps more broadly the Biden administration – figures that even if transmission isn't impacted, so long as the curve gets flattened, and people who get vaccinated are reasonably protected against severe COVID, then vaccination is a personal choi–

9.

2021 May 16: NYTimes: "The C.D.C. director offers a stark reassurance: Only unvaccinated people are at risk by unmasking." by Matt Richtel, Mitch Smith and Christina Morales:

The head of the Centers for Disease Control and Prevention, facing blowback over the agency’s new liberalized mask guidelines, offered a stark reassurance on Sunday: Only unvaccinated people are at risk if they take off their masks.

“If you are vaccinated, we are saying you are safe, you can take up your mask and you are not at risk of severe disease or hospitalization from Covid-19,” the C.D.C. director, Dr. Rochelle P. Walensky, said on “Fox News Sunday.” “If you are not vaccinated, you are not safe. Please go get vaccinated or continue to wear your mask.”

[...]

In her interviews on the Sunday news shows, Dr. Walensky revealed a subtle but marked shift in her agency’s emphasis from community to individual protection. She acknowledged on Fox that “for 16 months, we’ve been telling people to be cautious, be careful, cases are going up,” and made clear that the C.D.C.’s new bottom line is that individuals could make their own choices.

Huh. Well.

10.

But that's not all.

Above, I explained about the difference between IgA, the antibodies our bodies make in mucus that protects our upper respiratory system, and IgG, the systemic antibodies that protect most of the rest of us. I explained that we understand that intramuscular vaccination – getting a shot in the arm – provokes only IgG antibodies. And that this is why it was assumed that the protection one would get from the vaccines would protect the lungs and the rest of the body, but not the mucus membranes: because IgG doesn't show up in mucus.

2021 May 7: medRxiv [a preprint paper, not yet peer reviewed]: "Detection of persistent SARS-CoV-2 IgG antibodies in oral mucosal fluid and upper respiratory tract specimens following COVID-19 mRNA vaccination" by Mades et al.:

Previous studies have shown that mRNA COVID-19 vaccines are highly effective at preventing SAR-CoV-2 infection by generating an immune response, which in part produces SARS-CoV-2 IgG antibodies in serum. In this study, we hypothesized that COVID-19 vaccines may elicit production of SARS-CoV-2 IgG antibodies in the upper respiratory tract, such as in oral and nasal mucosal fluid. To test that hypothesis, we enrolled 114 participants within 3-7 days of receiving the first dose of the Moderna mRNA COVID-19 vaccine and collected oral mucosal fluid samples on days 5, 10, 15, and 20 after each vaccine dose. Of participants naive to SARS-CoV-2 (n = 89), 79 (85.4%) tested positive for SARS-CoV-2 IgG antibodies by time point 2 (10 days +/-2 days after first vaccine dose), and 100% tested positive for SARS-CoV-2 IgG by time point 3 (15 days +/-2 days after first vaccine dose). Additionally, we collected paired oral mucosal fluid and anterior nares samples from 10 participants who had received both vaccine doses. We found that participants had an average SARS-CoV-2 IgG antibody concentration of 2496.0 +/-2698.0ng/mL in nasal mucosal fluid versus 153.4 +/-141.0ng/mL in oral mucosal fluid. Here, we demonstrate detection and longitudinal persistence of SARS-CoV-2 IgG antibodies in upper respiratory tract specimens following COVID-19 mRNA vaccination.

The vaccine was Moderna.

Of participants naive to SARS-CoV-2 (n = 89), 79 (88.8%) tested positive for oral mucosa SARS-CoV-2 IgG antibodies by time point 2 (10 days +/-2 days after first vaccine dose), and 100% tested positive for oral fluid SARS-CoV-2 IgG by time point 3 (15 days +/- 2 days after first vaccine dose).

For this group, the average oral fluid IgG antibody concentration 20 days after the first vaccine dose (70.25 +/- 72.95ng/mL) was found to be significantly higher (p < 0.0001) than the average oral concentration at 5 days (1.517 +/- 0.25ng/mL). Further, the average concentration 20 days after the second vaccine dose (470.4 +/- 352.2ng/mL) was found to be significantly higher (p < 0.0001) than the antibody concentration observed 20 days after the first vaccine dose.

But what, you may wonder, about people who had natural infections with COVID?

Participants with prior SARS-CoV-2 infection not vaccinated against COVID-19

Self-collected oral fluid samples using the OSCD from the cohort of unvaccinated participants with a previous SARS-CoV-2 infection (n = 31) were evaluated over time (Fig. 3) 116 +/- 14 days following infection, the average concentration of SARS-CoV-2 IgG antibodies among these individuals was found to be 23.7 +/- 22.5 ng/mL.

So natural infection doesn't do it. But what about people who had COVID and then were vaccinated?

Of the 6 participants who were previously infected with SARS-CoV-2, 6 (100%) tested positive for SARS-CoV-2 IgG antibodies [in oral fluid] at time point 1 (5 days +/- 2 days). For this group, the average concentration 20 days after the first vaccine dose was 523.1+/- 548.6ng/mL and the average concentration 20 days after the second dose was 409.1 +/- 237.4ng/mL.

That's all oral samples. What about swabbing the nose?

Paired oral and nasal samples

In the subgroup of participants that provided a paired sample of anterior nares swab specimen and OSCD oral fluid specimen following their second vaccination dose (n=10), 100% of the anterior nare mucosa specimens had detectable antibodies with an average IgG antibody concentration of 2496.0 +/- 2698.0 ng/mL when adjusted for individual dilution factor.

Now at this point, I have questions I cannot yet answer. I have no idea what "2496.0 +/- 2698.0 ng/mL" means. As I understand that notation, one can't have a larger value to the right, because taken literally, it's saying it found IgG concentrations varying as low as negative 202.0 ng/mL. I'm pretty sure you can't have negtive amounts of antibodies. I'm given to understand we can't have negative amounts of any matter, except in economics and particle physics. That suggests I am not reading it correctly, I misunderstand something, or there's a typo. Even if it means "from 0 to 5194 ng/mL", I don't see how 0 or anything in its vacinity squares with "detectable levels".

If you can explain this, please do in the comments!

Also, even if we ignore the +/- part, and just focus on that 2496.0 ng/mL: is that a lot of IgG? It sure sounds like a lot, what with it being expressed as so many figures to the left of the dot. Do we even know? Have we detected IgG in mucus from any other vaccine, ever? Did we ever check? I put "IgG antibodies in oral mucosal samples" into Google and discovered that, yeah, IgG is understood to regularly leak a bit into the mouth from blood serum, and it's been considered as a potential non-invasive way to test for IgG serum levels, but I still had to get my arm punched to test for SARS-CoV-2 antibodies, and previously to test for MMR antibodies, which suggests to me that's still not widespread.

I did find a study on rubella-specific IgG in oral fluid, but to test its stability in vitro (here). Found total IgG concentrations ranged from 2.0 to 48.6 mg/l though. Note units: mg/l vs this study's ng/mL, but I think that is equivalent: that works out to the same number of grams per liter, yes? If so, this study is reporting an IgG response to Moderna an order of magnitude or two bigger than one sees in the saliva of people with IgG against rubella in their saliva, per this other study (which does not seem to say, at least in the abstract, how the subjects came by their rubella antibodies in the first place).

That's saliva; I got nothing on nasal secretions. On Google, the third hit on "IgG antibodies in nasal mucosal samples" has to do with rabbits, which is always a bad sign. The first hit is this study.

I am so far out of my lane it isn't funny, but my ignorant read on this is: boy, that's a lot of IgG SARS-CoV-2 antibody to find up people's noses. Like any seems to be a lot, and it's way more than none.

Does that mean it's effective in snot? Don't know. Not only don't I know...

High antibody concentration at the sites of the primary infection may play a direct role in preventing viral transmission.

...neither do the authors of the study. And it doesn't sound like they expect anybody else to know either.

Additional in-vitro experiments to study the effects of treating SARS-CoV-2 viral cultures with oral mucosal samples from vaccinated individuals would be required to test this hypothesis.

In other words, we'd have to test whether when someone sick with COVID-19 sneezes on a plate, if someone who had been vaccinated with Moderna spits on the plate it eradicates the virus there. This sounds, as medical studies go, really easy to conduct and somebody should get right on that because holy crap.

The mRNA vaccines (and for that matter the others) might cause sterilizing immunity. They might cause sterilizing immunity by causing SARS-CoV-2-specific IgG to show up in a place we really, really didn't expect it to: the part of the body usually protected by IgA, an antibody which we can't confer by intramuscular innoculation.

If this is true, we may have checkmated COVID.

11.

And, of course, if a vaccine provokes sterilizing immunity, or even just hampers transmission partially, we should see falling case numbers.

That is, of course, exactly what we're seeing.

2021 May 24: Reuters: "U.S. reports lowest number of new COVID-19 cases in nearly a year:

The United States last week reported the lowest number of new COVID-19 cases in nearly a year, with new infections dropping 26% from the previous seven days to just under 180,000, according to a Reuters analysis of state and county data.

Deaths from COVID-19 fell 5% to 3,969 in the week ended May 23, the fewest deaths in a week since March 2020. [...]

About 39% of the country's population has been fully vaccinated as of Sunday, and 49% has received at least one dose of a COVID-19 vaccine, according to the U.S. Centers for Disease Control and Prevention.

Vermont leads the country with 69% of its residents receiving at least one dose, followed by Massachusetts at 65%.

Here is a link to a heartening data visualization video on Twitter from @CovidActNow (Covid Act Now): US county map, daily new cases per 100k people, Jan-May 2021, to May 25.

Correlation, however, is not causation: we don't know this is due to the vaccine. As you may recall, there was a huge drop off in cases in Boston and NYC last May, too, raising the question – and it is a very good question – as to whether the drop off is a product of the change in weather.

I'm reasonably convinced that, throughout the pandemic, in the West we have pretty much completely failed to take seriously a whole class of factors in transmission that includes temperature, humidity, UV light, and air circulation (including ventilation). All of these have good scientific evidence of impacting droplets, aerosols, and/or SARS-CoV-2 in particular. These are apparently, like masks, taken seriously in Asia.

This is why I said I am concerned we may but be in the eye of the storm: there's a real possibility that the reduction in transmission we are seeing is a function of environmental conditions rather than vaccination.

That said, it was still full-on winter here in Boston when the vaccine rollout happened and the MWRA waste-water monitoring showed the level of SARS-CoV-2 falling off a cliff late January:

Of course, that might also be the populace responding with renewed social distancing efforts in the face of the horrendous holiday case spike that proceeded it.

But the trailing end of that graph is also intriguing. For both Moderna and Pfizer (the predominant vaccines being used here), it takes about six weeks from initial shot to full vaccination. The downward trend really starts around Apr 1, which counting back gets us to mid February, which was about when Phase 2 vaccinations started. Nothing happens from February through March, which looks like the vaccine not making much difference, but we can easily construct a story that explains that: the initial huge fall off in cases was because of how targetted the vaccine rollout was, inoculating healthcare workers and people living in congregate environments – populations very likely to transmit it to others – after which we had very limited amounts of vaccine which were administered to people who were very vulnerable (the elderly and the ill) who were not as likely to be vectors, and it was only as we began getting more vaccine into more low-transmissibility targets that we began to see the needle move. Maybe.

Or maybe it was the warming weather, the rising humidity, and the increased sunlight. Hard to say.

12.

But regardless of why it's happening, having less transmission means less opportunity for mutation. The observable drop in transmission, however we're coming by it, is tremendously good news.

13.

So it is not yet certain that vaccination is shutting down transmission of SARS-CoV-2. But we have a lot of reasons to expect vaccination will reduce transmission, at least somewhat, and good reason – even flabbergasting reason – to hope that vaccination all but eliminates it. It is possible that the vaccines reduce transmissions radically; we have tantalizing evidence that maybe the mRNA vaccines really do cause sterilizing immunity.

Meta note: this took rather longer to put together than I expected because while I was writing new science kept coming to my attention. This is a fast moving target! Obviously, there are a whole lot of scientists and public health authorities in the world focused very tightly on the question of figuring out what the vaccines do to transmission. So expect more news at any time. I am rushing this out the door before any more studies come out and it gets any longer.

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