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Transcript

Vaccines – How They Actually Work · Talking Science

• 0:00
  You know, I think we usually think of memory
• 0:02
  as like just a brain thing. Right. You touch
• 0:04
  a hot stove, your brain remembers the pain and,
• 0:07
  you know, never to do that again. Yeah. But your
• 0:10
  body on a microscopic level actually has a physical
• 0:14
  memory that operates entirely independently from
• 0:18
  your brain. Yeah, it really does. And realizing
• 0:21
  that fact back in the 18th century is essentially
• 0:23
  what allowed us to pull off what I think is the
• 0:25
  greatest biological heist in human history. So,
• 0:29
  welcome to the Deep Dive, everyone. Thanks for
• 0:31
  having me. And it really is a heist, honestly.
• 0:34
  Right. Today, our mission is to take a really
• 0:37
  comprehensive, untreated look at the fundamental
• 0:40
  science and the history of vaccines. We're stripping
• 0:43
  away the jargon so you can understand exactly
• 0:44
  how they work. Because we all hear about vaccines
• 0:47
  in the news, but, you know, understanding the
• 0:49
  actual mechanics gives you a completely different
• 0:51
  perspective. Oh, totally. It shows how... human
• 0:54
  ingenuity basically hijacked a natural biological
• 0:56
  process. Because if you survive a natural infection,
• 0:59
  you often can't catch that exact same disease
• 1:02
  again. Right. Because of that physical memory.
• 1:04
  Exactly. Specialized memory cells, B cells and
• 1:08
  T cells, they persist in your bloodstream and
• 1:10
  your bone marrow. They stick around sometimes
• 1:12
  for decades, just primed and ready to respond
• 1:15
  incredibly fast if that specific pathogen ever
• 1:18
  tries to return. So you get the memory and you
• 1:21
  get the protection. But the historical catch
• 1:23
  there was brutal. Right. Acquiring that memory
• 1:25
  the natural way meant you actually had to survive
• 1:28
  the disease first. Yeah, that was a catch. And
• 1:30
  for most of human history, that meant facing
• 1:32
  a very, very meaningful chance of death or just
• 1:35
  permanent life -altering harm. You essentially
• 1:37
  had to gamble. your life for the immunity. Which
• 1:40
  is why the whole concept of a vaccine is so elegant.
• 1:43
  At its core, I mean, it is simply a way of obtaining
• 1:45
  that specific immune memory without having to
• 1:48
  endure the actual illness. You get the memory,
• 1:52
  but you skip the disease. Skip the line entirely.
• 1:54
  Exactly. And what's fascinating is that the history
• 1:57
  of this breakthrough starts entirely with observation,
• 1:59
  like long before we had any actual scientific
• 2:01
  theory to explain it. We really have to go back
• 2:04
  to an 18th century English country doctor for
• 2:06
  this, Edward Jenner. Right. He didn't have a
• 2:08
  microscope. He had no concept of genetics, obviously.
• 2:10
  Yeah. But he paid attention to this widespread
• 2:13
  piece of local folk knowledge. People noticed
• 2:16
  that milkmaids, you know, the women who milked
• 2:18
  cows for a living, frequently caught a mild disease
• 2:21
  called cowpox from the cattle. Yeah, just a mild,
• 2:24
  annoying rash, really. But the crucial observation
• 2:27
  was that. Milkmaids who were covered from cowpox
• 2:30
  seemed entirely bulletproof against smallpox.
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  And smallpox was no joke. Oh, smallpox was an
• 2:36
  absolute terror. When you look at the historical
• 2:38
  data, it was killing roughly a third of the people
• 2:41
  it infected. Wow. One in three. One in three.
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  And for those who did survive, it routinely left
• 2:45
  them permanently disfigured or even blind. It
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  was devastating. So in 1796... Jenner just decides
• 2:52
  to test this folk knowledge. He takes material
• 2:54
  from a cowpox sore, inoculates a young boy, lets
• 2:58
  him recover from the mild cowpox, and then deliberately
• 3:00
  exposes the boy to smallpox. Which is pretty
• 3:03
  wild by today's ethical standards. Very wild.
• 3:05
  But the boy didn't get ill. Jenner proved the
• 3:08
  concept. And just as a quick side note for you
• 3:11
  listening, the word vaccine actually comes directly
• 3:14
  from this experiment. Yes, it derives from vacca,
• 3:17
  which is the Latin word for cow. Right. In honor
• 3:19
  of the cowpox. Yeah. It makes me think of like
• 3:21
  using a smartphone today. How so? Well, you can
• 3:24
  hand a phone to someone and they don't need to
• 3:26
  understand anything about microchips or wireless
• 3:29
  frequencies or, you know, the binary code to
• 3:31
  make a call. They just need to figure out which
• 3:34
  buttons to push on the screen to get a reliable
• 3:36
  result. Oh, I see. Jenner essentially found the
• 3:39
  biological buttons to push, even though immunology
• 3:42
  literally didn't exist as a science yet. That
• 3:44
  is a great way to frame it. He found the interface
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  but he didn't know the code. Germ theory, the
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  idea that microscopic organisms cause disease,
• 3:54
  that was still decades away. Decades. Yeah. But
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  that observation was enough of a foundation to
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  build on. And just to fast forward to the ultimate
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  conclusion of Jenner's work, smallpox was officially
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  declared eradicated in 1980. Which is incredible.
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  It is. It remains the only human disease we have
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  ever deliberately wiped off the face of the earth.
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  So Jenner gave us the effect. But what is the
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  actual biological mechanism inside the body?
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  Because once we started to understand the code,
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  the underlying cellular mechanics, we didn't
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  have to rely on lucky accidents like cowpox anymore.
• 4:27
  Right. We could start engineering the interface
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  ourselves. Exactly. We had to figure out how
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  to give the immune system a target. And that
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  target is called an antigen. The goal here is
• 4:37
  obtaining immune memory without the illness,
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  right? Right. So think of the antigen as the
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  active ingredient. It's a specific molecular
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  structure, usually a protein on the surface of
• 4:48
  a virus or bacteria, that looks enough like the
• 4:51
  dangerous pathogen for your immune system to
• 4:53
  learn from it. But it's incapable of causing
• 4:56
  the disease itself. Precisely. It's safe training
• 4:58
  data. And over the years, we've basically developed
• 5:01
  four main engineering strategies to deliver this
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  training data. OK, let's break those down because
• 5:07
  I have a sort of fire training analogy in mind
• 5:09
  for these four types. Oh, I like analogies. Let's
• 5:11
  hear it. OK, so the oldest method we have is
• 5:14
  the live attenuated vaccine. In my analogy, this
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  would be like putting the fire department through
• 5:19
  a controlled burn. It's a real fire, but it's
• 5:22
  artificially contained. That is highly accurate,
• 5:25
  actually. Attenuated just means weakened. So
• 5:27
  you take the real life pathogen and you grow
• 5:30
  it in a lab under very specific conditions. Or
• 5:33
  weaken it. Right. You force it to mutate and
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  adapt to an alien environment. By the time you
• 5:38
  put it into a human, it's so weak that it replicates
• 5:41
  very, very poorly. In vaccines like measles,
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  mumps, rubella. They're designed this way, right?
• 5:46
  Yes. And chickenpox, too. Because it's a real
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  replicating infection, the immune response is
• 5:51
  massive. The memory it forms is typically lifelong.
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  I mean, a couple of doses of the measles vaccine
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  and you're usually set for decades. But there's
• 5:59
  a tradeoff there. Because a live virus, even
• 6:02
  a weakened one, is still a replicating threat.
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  So you can't give a controlled burn to a force
• 6:07
  that's completely dried out. Exactly. You wouldn't
• 6:09
  give a live attenuated vaccine to someone with
• 6:11
  a severely compromised immune system, like a
• 6:14
  patient undergoing chemotherapy. So to protect
• 6:16
  them, you need strategy number two, which are
• 6:19
  inactivated vaccines. And in our fire training
• 6:22
  analogy, this would be like having the fire department
• 6:24
  practice putting out a completely fake dummy
• 6:27
  fire. There's no heat, no real danger at all.
• 6:30
  Spot on. With inactivated vaccines, you take
• 6:33
  the pathogen and you completely destroy its ability
• 6:35
  to replicate, usually using heat or radiation
• 6:38
  or chemicals. So the structure is there, but
• 6:41
  it's dead. The physical structure is intact for
• 6:43
  the immune system to recognize. But yes, the
• 6:46
  pathogen is dead. But that creates a new tradeoff.
• 6:48
  It is much safer. But because the pathogen isn't
• 6:51
  replicating, the immune system doesn't mount
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  nearly as aggressive a response. Because it doesn't
• 6:55
  view it as a five alarm fire. Right. The memory
• 6:58
  it forms is weaker. Because of that, inactivated
• 7:01
  vaccines like the polio shot or the rabies vaccine,
• 7:05
  they usually require multiple doses or boosters.
• 7:07
  Just to remind the immune system of the threat.
• 7:10
  OK, so if a dead virus gives a weaker signal
• 7:12
  anyway, do we even need the entire virus body?
• 7:16
  Strategy number three is subunit vaccines, which
• 7:19
  I imagine is like instead of a dummy fire, you
• 7:22
  just bring the firefighters a single piece of
• 7:24
  a burnt log to study. That's a perfect way to
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  visualize it. You abandon the whole organism
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  entirely. You just use a single fragment like
• 7:32
  a highly characteristic surface protein. And
• 7:34
  that's things like the hep B and HPV vaccines.
• 7:37
  Yes. It is incredibly safe because there is zero
• 7:40
  genetic material from the pathogen. It physically
• 7:42
  cannot replicate. But the biological hurdle here
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  is that if you just inject a harmless little
• 7:47
  piece of a burnt log into the muscle, the immune
• 7:50
  system might just ignore it entirely. It doesn't
• 7:52
  look dangerous enough to care. Exactly. So you
• 7:54
  have to manufacture a sense of danger. And you
• 7:56
  do that using an ingredient called an adjuvant.
• 7:59
  An adjuvant. OK, what is that? They're fascinating.
• 8:01
  They are specific compounds, sometimes aluminum
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  salts or synthetic molecules, that basically
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  mimic the biochemical danger signals of a real
• 8:10
  infection. So they act like local fire alarms.
• 8:12
  Yes. They create a localized, harmless irritation
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  at the injection site. This triggers cellular
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  alarms that physically recruit specialized immune
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  cells to rush to the area. And when they show
• 8:25
  up to investigate the alarm, they bump into the
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  burnt log. They bump into the protein fragment,
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  recognize it as foreign, and carry it back to
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  the lymph nodes to build the memory. Wow. OK,
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  so we've gone from a controlled burn to a dummy
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  fire to studying a burnt log. But strategy number
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  four, mRNA, which obviously gained massive prominence
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  during COVID, is a totally different ballgame.
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  It is a profound conceptual shift. Yeah. In my
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  analogy, mRNA isn't a fire at all. It's like.
• 8:54
  emailing the fire department a detailed blueprint
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  of the exact weapon an arsonist is planning to
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  use so they can build a harmless model of it
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  themselves. That is a great analogy. We are no
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  longer delivering the antigen. We are delivering
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  the instructions for the antigen. The vaccine
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  contains a strand of messenger RNA, which is
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  essentially just a line of genetic code. It holds
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  the precise recipe for building one single protein
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  from the pathogen. But RNA is super fragile,
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  isn't it? Highly fragile. It would be destroyed
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  instantly in the bloodstream. So it's wrapped
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  in a microscopic bubble of fat called a lipid
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  nanoparticle. This fat bubble merges with your
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  cells, slipping the mRNA code inside. So your
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  own cells read the instructions and manufacture
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  the single protein. Mechanically execute the
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  code, yes. They print out the viral protein,
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  push it to the surface of the cell, and your
• 9:40
  immune system spots it and learns it. And we
• 9:43
  really need to pause and debunk a massive myth
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  here. Because this exact mechanism is... why
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  the common fear that mRNA alters your DNA is,
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  well... Biologically impossible. Completely impossible.
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  Your DNA is stored inside a highly secure locked
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  vault in the center of the cell called nucleus.
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  For a molecule to get inside, it requires very
• 10:03
  specific molecular passcodes. Passcodes that
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  the vaccine mRNA simply does not have. It doesn't
• 10:08
  have them. It physically cannot cross into the
• 10:10
  nucleus. And furthermore, your cells are packed
• 10:12
  with enzymes whose entire job is to hunt down
• 10:15
  and shred free -floating RNA. Within a matter
• 10:17
  of days, the vaccine mRNA is completely degraded
• 10:20
  and recycled. It leaves zero trace. Zero trace.
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  But the huge advantage of mRNA is speed. Because
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  it's just code, you don't need giant vats to
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  grow live viruses over months. You just need
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  a chemical synthesizer. So you can design a candidate
• 10:35
  in days from a genetic sequence. Over a single
• 10:39
  weekend, theoretically. That's incredible. Now,
• 10:41
  because these vaccine types differ in strength
• 10:43
  and design, they don't all last the same amount
• 10:46
  of time. Which brings us to why some vaccines
• 10:48
  are one and done and others require you to keep
• 10:51
  coming back for boosters. Right. There are three
• 10:53
  main reasons immunity fades or fails. The first
• 10:56
  is that the pathogen itself mutates fast. Like
• 10:59
  the flu. Influenza is the master of this. Its
• 11:03
  surface proteins are constantly shifting. The
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  facial recognition software you trained last
• 11:07
  year is looking for a suspect that just doesn't
• 11:09
  exist anymore. That is why the flu shot requires
• 11:12
  annual reformulation. Whereas measles is genetically
• 11:14
  stable. Highly stable. Its face doesn't change,
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  so childhood immunity stays relevant your entire
• 11:19
  life. The second reason goes back to the engineering
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  trade -offs. The vaccine type might just provoke
• 11:24
  a weaker memory, like we saw with inactivated
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  versus live vaccines. Exactly. And the third
• 11:30
  reason is just that immune memory naturally wanes
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  over time. Tetanus is the classic example here.
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  Your antibody levels drop over the years, so
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  you need a booster roughly every decade. OK,
• 11:41
  that makes sense. Now, I want to clarify something
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  about how we measure the effectiveness of these
• 11:45
  vaccines, because the statistics are routinely
• 11:48
  misunderstood. Oh, absolutely they are. You'll
• 11:50
  read a headline saying a new vaccine is 95 percent
• 11:53
  effective. And I think the intuitive leap people
• 11:56
  make is absolute risk. They think, OK, if 100
• 11:59
  vaccinated people are exposed, 95 are perfectly
• 12:02
  safe and five will get sick. And that is mathematically
• 12:05
  incorrect. Right. It means a relative reduction
• 12:07
  in risk, doesn't it? Let me try another analogy
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  here. Let's look at seatbelts. Okay. If I tell
• 12:13
  you a seatbelt is highly effective, I'm not guaranteeing
• 12:16
  that in 100 car crashes, you will walk away without
• 12:19
  a scratch 95 times. Definitely not. What I'm
• 12:22
  telling you is that wearing the seatbelt drastically
• 12:24
  reduces your relative risk of suffering a fatal
• 12:27
  injury compared to a driver who isn't wearing
• 12:29
  one. That is exactly how vaccine efficacy works.
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  The vaccinated group experienced 95 % fewer cases
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  than the unvaccinated group under the same exposure.
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  And that distinction highlights something critical.
• 12:43
  You have to look at what outcome is actually
• 12:45
  being measured. Right. Preventing infection altogether
• 12:47
  versus preventing severe disease. Exactly. Headlines
• 12:50
  often confuse the two. A vaccine might only be
• 12:53
  moderately effective at preventing you from getting
• 12:55
  the sniffles. But that exact same vaccine might
• 12:58
  be incredibly effective at preventing severe
• 13:00
  disease, hospitalization and death. Which is,
• 13:03
  you know, generally the primary public health
• 13:05
  goal. Keeping you out of the ICU. Is a massive
• 13:09
  victory. Exactly. And understanding that this
• 13:11
  is about risk reduction on a grand scale leads
• 13:14
  us perfectly into what happens when you zoom
• 13:16
  out from the individual and look at an entire
• 13:18
  community. Herd immunity. Yes. Herd immunity.
• 13:20
  It breaks the chains of transmission. It's the
• 13:23
  ultimate mathematical shield. It protects those
• 13:25
  who literally can't be vaccinated. Newborns,
• 13:28
  chemotherapy patients, people with immune conditions.
• 13:31
  But the math behind it depends heavily on the
• 13:33
  specific disease, right? Yeah. There's a metric
• 13:35
  called R -naught. Right. R -naught. or R0. It's
• 13:39
  the average number of people one infected person
• 13:42
  would infect in a fully susceptible population.
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  And the formula for the required immune threshold
• 13:47
  is basically 1 minus 1 over the R0. So let's
• 13:50
  look at measles. Measles is astonishingly contagious.
• 13:53
  It has a massive R -naught of 12 to 18. One person
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  infects up to 18 others. Wow. So if you plug
• 14:01
  an R -naught of 18 into that formula, the required
• 14:03
  immune threshold for the population sits at roughly
• 14:05
  95%. Which means the margin for error is razor
• 14:08
  thin. That's exactly why measles is the very
• 14:11
  first disease to return when vaccination coverage
• 14:14
  in a community slips even a little bit. Because
• 14:16
  the shield cracks. Now speaking of... Speaking
• 14:19
  of the shield, I want to pause and talk about
• 14:20
  the physical experience of actually participating
• 14:22
  in that shield, because we shouldn't dodge the
• 14:25
  reality of side effects. We absolutely shouldn't.
• 14:27
  When I get a shot, I often get a sore arm. I
• 14:29
  feel exhausted and I might even run a mild fever
• 14:31
  for a day. And instinctually, my brain says,
• 14:34
  well, the vaccine is making me sick. It's a natural
• 14:37
  instinct, but it's biologically backward. A sore
• 14:40
  arm, tiredness, or a mild fever is not the vaccine
• 14:43
  going wrong. It is your immune system responding,
• 14:46
  which is the whole point. Wait, so if the fever
• 14:49
  and sore arm are just proof that my immune system
• 14:51
  is taking notes, should I actually be happy that
• 14:53
  I feel a little crummy for a day? Is feeling
• 14:55
  gross actually a success story? Yes, absolutely.
• 14:59
  It is the biopemical proof that your immune system
• 15:02
  is successfully executing the training drill.
• 15:04
  Okay, that changes my perspective completely.
• 15:07
  But we do need to address serious adverse events,
• 15:10
  too. We do. And acknowledging them is vital.
• 15:12
  Serious adverse events genuinely do happen, but
• 15:15
  they are incredibly rare. We are talking one
• 15:17
  in hundreds of thousands to one in a million
• 15:19
  doses. And we have systems to track that, right?
• 15:22
  Very mature global surveillance systems. If a
• 15:25
  risk emerges, it's caught. But the key is that
• 15:27
  the risk of the disease itself is always much,
• 15:29
  much higher. And while we're talking about safety,
• 15:32
  we have to debunk the MMR autism myth. Because
• 15:36
  it's still out there. It stems entirely from
• 15:38
  a retracted 1998 paper. By one doctor. Yes. And
• 15:42
  when you look at it, it was based on just 12
• 15:44
  children. 12. That's a tiny sample size. It is.
• 15:48
  Furthermore, he had undisclosed financial conflicts
• 15:51
  of interest. He eventually lost his medical license
• 15:54
  and the journal formally retracted the paper.
• 15:56
  And what have the studies shown since then? Subsequent
• 15:59
  studies of millions of children across multiple
• 16:01
  countries show a totally consistent answer. There
• 16:05
  is absolutely zero association between vaccines
• 16:08
  and autism. So when safety, high effectiveness
• 16:11
  and mass population uptake align perfectly, we
• 16:14
  can aim for that holy grail of epidemiology we
• 16:17
  mentioned earlier, making the pathogen disappear
• 16:19
  forever. Eradication. Why was smallpox eradicated
• 16:23
  but not other diseases? Because three specific
• 16:25
  conditions have to line up. Condition one. It
• 16:28
  must infect only humans. There can't be an animal
• 16:31
  reservoir to hide in. Makes sense. If it lives
• 16:33
  in bats or pigs, it'll just keep coming back.
• 16:35
  Exactly. Condition two, the infection must be
• 16:37
  visibly identifiable so public health workers
• 16:40
  can contain cases. And condition three is obviously
• 16:43
  an effective vaccine. Right. Now, polio nearly
• 16:47
  meets all three. We have pushed it to the absolute
• 16:49
  brink. But human conflict and access difficulties
• 16:53
  in remote areas make that final step stubbornly
• 16:56
  hard. And then contrast that with influenza.
• 16:59
  Influenza fails the first condition entirely.
• 17:02
  It lives in birds and pigs, continually mutating
• 17:05
  and reentering human populations. We can't eradicate
• 17:09
  it with current tech. So let's bring it all together
• 17:11
  for everyone listening. Vaccines basically exploit
• 17:14
  a biological quirk of our immune memory. We've
• 17:17
  gone from a country doctor observing milkmaids
• 17:19
  to literally delivering genetic instructions
• 17:22
  inside lipid nanoparticles. And all of it is
• 17:25
  designed to reduce relative risk and protect
• 17:27
  the vulnerable members of the herd. It really
• 17:29
  is an amazing journey. But before we wrap up,
• 17:31
  I want to leave you, the listener, with a really
• 17:33
  fascinating thought to mull over. We talked about
• 17:35
  the mRNA timeline. The speed of it. Right. If
• 17:38
  mRNA technology allows us to design a vaccine
• 17:41
  candidate in a matter of days simply from a genetic
• 17:43
  code, what does that mean for the next time a
• 17:46
  pathogen tries to jump from an animal reservoir
• 17:48
  to humans? It's a huge question. Could we theoretically
• 17:51
  reach a point in the future where we have the
• 17:53
  vaccine ready before the first major outbreak
• 17:56
  is even officially noticed? To essentially stop
• 17:59
  the pandemic before it ever really starts. It's
• 18:02
  an incredible prospect. It really gives you hope
• 18:04
  for the future. Well, that's all for today's
• 18:06
  deep dive. Thanks for listening, and we'll see
• 18:08
  you next time.