What happens if a vaccinated person inhales some Delta coronavirus?

August 3, 2021 9:03 PM

Suppose a person who is vaccinated, inhales "some" coronavirus-laden droplets. Surely that must happen -- it has probably even happened to me. (Perhaps it happens all the time?) How can one tell? Is it possible to distinguish between "living a pure life far from anyone who has even heard of the virus and definitely not inhaling any of it" and "partying at all the bars in Covid Central but miraculously never getting sick"?

Someone must have wondered this already, but I can't convince Google to dig it up for me.

I can imagine a range of exposures and possible results, but I don't know enough biology to fill in the details. Can you help?

1. Inhale a few particles, but not even enough for an unvaccinated person to get sick.
2. Inhale more particles, or a few particles enough times within a particular timespan. This surely happened before the vaccines became available, but not everybody got sick. What happened?
3. Inhale even more, where you'd probably get sick if you were unvaccinated. But you're vacccinated...it seems that Delta can get established in the sinuses enough that you can become contagious, even though you don't get really sick. Do you know that it's there? Do you get a little sick? Do you have actual cold symptoms, or do you have maybe one weird sneeze that might be because you walked out into the sun? Can you tell that it was a Delta infection that was knocked back by the vaccine and not just a regular cold?

Which of these can one detect? How would it be detected?

Is there a detectable difference between somebody living at 1 or 2 and somebody who's been off-planet for the past few years?

Is the virus circulating widely enough that everybody in the world is at 1 all the time?

posted by spacewrench to Health & Fitness (12 answers total)

I follow COVID research pretty closely and the best that I can come up with to tell you right now is that we are still trying to figure this out. I have been trying to explain to people that the initial emergency use authorization for the existing COVID vaccinations was based on studies that used an endpoint of essentially avoiding serious illness and hospitalization. It wasn’t until some months later that we had data that vaccinated individuals seemed to be less likely to be capable of being infected and/or transmitting COVID particles (this is, of course, from the earlier variants).

The best that I have been able to sort out is that there is some emerging evidence that people who are vaccinated have been shown to be able to harbor COVID delta variant viral particles in their respiratory tract (which can then replicate), and are capable of being infected with delta variant COVID, which accounts for the increased number of breakthrough infections. However, it does also seem that the number of vaccinated individuals who end up hospitalized from delta is much lower than those who are unvaccinated. I don’t think we have data yet on what sort of “dose” of COVID delta particles are required for someone to become infected.

To your third point, it’s really hard to tell, because you wouldn’t generally get tested if you weren’t feeling ill, unless there was some event that you needed to show proof of a negative COVID test (and most immunized individuals aren’t required to show proof of a negative test if they have proof of vaccination at this point).

I work daily in clinics and hospitals and have continued to mask indoors at all times unless I am in a room by myself with the door closed. Haven’t gotten sick, and haven’t had a positive antibody blood test (different than a spike antibody which tests vaccine response). My spouse has been teaching from home for the last 3 semesters, in part to decrease the likelihood that he becomes infected, gives it to me, and then I spread it inadvertently to my very immunocompromised patient population. We started dining indoors about once a week in April. In Texas, I would estimate that we are in the top 10th percentile of cautiousness. I remain hopeful that continued masking keeps me at a “1.”
posted by honeybee413 at 9:49 PM on August 3, 2021 [10 favorites]

I'm not totally sure this addresses your question, but an exposure that doesn't make you sick can still be detected - e.g. by testing that detects an asymptomatic infection, or by antibody testing that shows a response to different antigens than were in the vaccine, which would show some additional exposure.

If you inhaled two virus particles that just got caught in your nose mucus and died there, though, that's the same as if they got caught in your face mask and died, or landed in your hair. Not detectable.
posted by Lady Li at 10:28 PM on August 3, 2021 [3 favorites]

Experience rather than science; I was fully vaccinated (Pfizer) and tested positive for coronavirus + was symptomatic 4 weeks later. I thought I had really really bad allergies, but I dropped a bottle of lavender essential oil and realised I couldn't smell it. As I'm in the UK, chances are extremely high that it was Delta.
posted by socky_puppy at 12:08 AM on August 4, 2021 [3 favorites]

Best answer: For an in depth view of the research elements which underly your question - you could look at a paper like "Transmission of COVID-19 virus by droplets and aerosols: A critical review on the unresolved dichotomy"- this particular paper is from September last year and somewhat pre-dates 2021's emphasis on the differing infection profiles of different variants - and of the effects of vaccinations.

This December 2020 paper from Nature (Size distribution of virus laden droplets from expiratory ejecta of infected subjects) attempts to answer your specific question, which I understand as something like "how many virus laden droplets do you have to inhale to become infected?" It tells that virusol concentrations of less than 2 × 105 RNA copies/mL are "unlikely to be of consequence to carrying infections". Since that time, again, we need to consider the case for more infectious variants like delta - as well as the protective effect of vaccines. What is definitely agreed here is that there is indeed a certain amount of viral particles that you can inhale without getting infected - but subject to a whole raft of caveats about your individual susceptibility, the size of the drops, how deeply you inhale them and the concentration of the virus in the drops.

The final, and fairly big, unknown here seems to be a consideration of those people who simply don't get Covid 19 - never did and maybe never will. Researching these people comes well down the priority list in a pandemic where the focus is on treating patients, preventing infections and vaccine development - but it looked like maybe 20% of the population were falling into this category last year. Since then many of those people will have been vaccinated anyway. It is a fairly large and mysterious group - and it could indeed include those who could party in all the bars of Covid central with impunity.
posted by rongorongo at 3:29 AM on August 4, 2021 [4 favorites]

My understanding is that even for much more established illnesses such as influenza, the exacts of transmission are more in the realm of speculation and hypothesis than tested proof.
I suspect that quantity of viral exposure is less like a water level overtopping a dam, and more like buying an immense number of lottery tickets. That is, there are likely levels where incidental exposure is vanishingly unlikely to cause infection, and levels where infection becomes increasingly likely, but probably not a single threshold where the count of viral particles switches from “safe” to “dangerous”.
posted by meinvt at 4:20 AM on August 4, 2021 [10 favorites]

I follow Covid science and the delta news very closely. Delta doesn't behave much differently than the rest of covid, only a few variables change.

My understanding of what happens when your body gets ANY virus is this:

1. Some number of virus particles enter your body.
2a. Your immune system begins to react. It tries many things. If it has encountered a similar virus before, it tries those things first and more strongly.
2b. (simultaneously) The virus rapidly multiplies, by injecting their DNA in your cells, which fill with virus until it explodes.
3. If 2b outpaces 2a, you have so much virus in your body, that large amounts float out in every exhalation.
4. Eventually, your immune system kills the virus in your body.

Think of 2b (Virus multiplication) and 2a (immune system response) as a tug of war in the body. There's different factors that will help either side progress. And, anytime 2b outpaces 2a, it leads to an infection.

Things that help 2b:

Large viral dose (amount of virus up front)
Slow or unlucky Immune System
Bad Immune System Memory of previous encounters
Delta / faster multiplication

Things that help 2a
Small viral dose
Vaccines, helping memory
posted by bbqturtle at 5:57 AM on August 4, 2021 [7 favorites]

I've started watching some YT videos with Dr. Daniel Griffin going over recent research papers. Recent example here. One of the things I've learned is that there is a distinction between getting infected and getting sick. The percent numbers we see for vaccine protection are for getting sick.

Infection can be detected via a blood test in patients who have not yet developed symptoms, but it's not what is helpful outside the lab.
posted by SemiSalt at 6:30 AM on August 4, 2021 [2 favorites]

Best answer: The term "get sick" is confusing and potentially misleading. Here's a way to look at the spectrum of possibilities without using that term.

1. Inhale some COVID particles. You have been EXPOSED to COVID-19. You may or may not get an infection. If the virus can't reproduce in your body, you don't get an infection. Stop here.

2. The virus begins reproducing in your body. You are now INFECTED with COVID-19. You may or or may not develop symptoms ("get sick") and you may or may not produce enough of the virus to infect other people.

Once you are infected, it gets more interesting:

3.a. The virus is able to reproduce some but not a lot. Your infection remains ASYMPTOMATIC (you don't "get sick"). You may or may not be able to transmit the disease to other people.

3.b. The virus reproduces enough that you are able to infect other people. You may or may not experience symptoms. If you don't experience symptoms, you are asymptomatic but can still spread the disease.

3.c. The virus reproduces enough that you experience symptoms. You are now "sick with COVID-19". You also now have enough of the virus in your system that you can transmit the disease to other people.

Once you are sick with COVID-19, there's a whole range of possibilities, from very mild, to super sick at home, to hospitalized, to death.

I am not an infectious disease specialist, and I don't know if "infected with COVID-19" versus "sick with COVID-19" is exactly the right terminology, but I believe it's a very important distinction to make in order to understand the situation.
posted by Winnie the Proust at 7:52 AM on August 4, 2021 [10 favorites]

I am as much an epidemiologist as anybody living in this Pandemic(i.e., not at all, just read news and MeFi and articles). I think the term you want is viral load; a measurement of the amount of a virus in an organism, typically in the bloodstream, usually stated in virus particles per milliliter. If you get a smaller exposure to many viruses, your immune system is able to stop the virus. More viral particles = greater likelihood and severity of illness. It's my understanding that this matters a lot with Covid, not sure about Delta variant. People with weaker immune systems and more co-morbidities are at correspondingly higher risk.

Someone living without any exposure at all to flu, colds, etc, might have less resistance to some flu or other viral strains because their immune system is out of practice?
posted by theora55 at 9:50 AM on August 4, 2021 [1 favorite]

Best answer: I somewhat disagree with Winnie's options. I've made some notes below. Overall a great layout of possibilities but a few important details seem off.

1. Inhale some COVID particles. You have been EXPOSED to COVID-19. You may or may not get an infection. If the virus can't reproduce in your body, you don't get an infection. Stop here. technically exposure doesn't necessitate inhalation - being in the same room with someone but not inhaling it is also an exposure.

2. The virus begins reproducing in your body. You are now INFECTED with COVID-19. You may or or may not develop symptoms ("get sick") and you may or may not produce enough of the virus to infect other people.

Once you are infected, it gets more interesting:

3.a. The virus is able to reproduce some but not a lot. Your infection remains ASYMPTOMATIC (you don't "get sick"). You may or may not be able to transmit the disease to other people. This one is the major one I have a contention with. The amount of virus in someone's body isn't completely related to if you show symptoms or not. The symptoms of covid are related to how your immune system responds, not the quantity of covid in your body.

3.b. The virus reproduces enough that you are able to infect other people. You may or may not experience symptoms. If you don't experience symptoms, you are asymptomatic but can still spread the disease.

3.c. The virus reproduces enough that you experience symptoms. You are now "sick with COVID-19". You also now have enough of the virus in your system that you can transmit the disease to other people. Again, the symptoms aren't related to the amount of virus, it's the amount of immune system response.

Once you are sick with COVID-19, there's a whole range of possibilities, from very mild, to super sick at home, to hospitalized, to death.
posted by bbqturtle at 9:51 AM on August 4, 2021 [2 favorites]

Response by poster: Thanks, everyone. It's helpful to have a framework (such as this and this) for thinking about waypoints along a continuum. Thanks also to rongorongo for some recent scientific papers that (probably) you have to ask Google about in a special way if you want to find them. I wouldn't have guessed that "droplets" vs. "aerosol" was as interesting as it seems to be (from a lay perspective, it seems like boffins arguing about angels on the heads of pins) but on reflection, you certainly want to know whether all the virus that contagious people are horking out remains floating around in the air or falls to the ground.

There are plenty of other things a layperson might be curious about (such as the "symptoms reflect immune system response:" if you don't mount a response at all, could you still die of COVID because enough cells become infected and "explode?" [great visual!]) But I can see that a lot of those things are either not on the main thread of research into "how to keep people from getting COVID" or "how to keep symptomatic people alive," or are harder to investigate and nobody has had time to look yet. So "we don't know yet (and may never find out)" is a totally plausible answer for many questions.
posted by spacewrench at 10:27 AM on August 4, 2021 [1 favorite]

We are all •exposed• to countless viruses and bacteria all day, every day, for our entire lives[1]. If you’ve been close enough to someone to smell their breath, you’ve been exposed to all sorts of things.

The vast majority of the time, we are not •infected• by any of these exposures. Our immune system constantly surveils us and destroys wayward germs before we ever know they were there. For people of normal immunocompetence, this system fails very infrequently—maybe once or twice a year? And we end up with a cold or a stomach bug or what have you.

And many, if not most, of the things that people feel when they are sick are not a result of the pathogen itself but of the immune system’s response to the pathogen. Fever, body aches, fatigue, etc., are all caused by the immune system. That’s why feeling crappy after the vaccine was a feature, not a bug—it showed that the immune system was recognizing and mounting a defense against the bad guy.

[1] Many things have surprised me during this pandemic but nothing quite so much as the realization that lots of people genuinely seemed to believe that they were living in a sterile bubble before covid came along. The idea that maybe they should have always washed their hands with soap and water for 20 seconds after using the bathroom and before eating seems never to have occurred to them.
posted by jesourie at 10:45 AM on August 4, 2021 [4 favorites]