A2 · Elementary
11 min
healthsciencehistorysociety
Cómo funcionan las vacunas
How Vaccines Work
Fletcher breaks down this story in English. Octavio reacts and expands in Spanish. Follow along with the live transcript, tap any word for its translation. Elementary level — perfect for beginners building confidence.
So today we're going into something that touches pretty much every single person alive on this planet.
Vaccines.
And I know that sounds like a dry topic, but I promise you, by the end of this, you're going to be genuinely surprised by how much there is to say.
Bueno, las vacunas salvan millones de vidas.
Vaccines save millions of lives.
Son muy importantes.
They are very important.
Millions of lives, Octavio says, and that is not an exaggeration.
We're talking about one of the most consequential medical inventions in human history.
But let's start simple, right.
What is actually happening inside your body when you get a vaccine?
Mira, el cuerpo tiene un sistema de defensa.
The body has a defense system.
Lo llamamos el sistema inmune.
We call it the immune system.
The immune system.
Right.
And most of us know that phrase, but I think very few of us really understand what it does.
So, walk me through it.
What is this defense system actually made of?
A ver, tenemos glóbulos blancos en la sangre.
We have white blood cells in our blood.
Ellos atacan los virus y las bacterias.
They attack viruses and bacteria.
White blood cells.
Little soldiers, basically, circulating through your bloodstream, looking for anything that doesn't belong.
And here's the thing, the first time they encounter a new enemy, they don't always win fast enough.
That's where vaccines come in.
Exacto.
Exactly.
La vacuna enseña al cuerpo.
The vaccine teaches the body.
El cuerpo aprende a luchar.
The body learns to fight.
It teaches the body to fight.
So it's almost like...
a training exercise?
You're introducing a safe version of the enemy so the immune system can practice, can build a memory, before the real thing shows up.
Sí, es exactamente eso.
Yes, that's exactly it.
Es un entrenamiento para el sistema inmune.
It's training for the immune system.
And once your immune system has that memory, that blueprint, it can respond incredibly fast when the real pathogen arrives.
We're talking hours instead of days.
That speed is the difference between a mild illness and, in many cases, death.
So, let's talk history, because this story goes back further than most people think.
Bueno, la primera vacuna es del siglo dieciocho.
The first vaccine is from the eighteenth century.
Un médico inglés la inventa.
An English doctor invents it.
Edward Jenner, 1796.
And here's what gets me about this story: the insight didn't come from a laboratory.
It came from talking to farmers.
Jenner noticed that milkmaids who caught cowpox, a mild disease, never seemed to get smallpox.
Which was, at the time, one of the most deadly diseases in the world.
La palabra vacuna viene de vaca.
The word vaccine comes from cow.
La verdad, es muy interesante.
Honestly, it's very interesting.
The extraordinary thing is, I knew the word vacuna, I'd heard it a thousand times, and I had never once made that connection.
Vacuna, vaca, vaccine, cow.
Jenner literally named the whole concept after the animal that gave him the clue.
That's remarkable.
Mira, en latín, vacca significa vaca.
In Latin, 'vacca' means cow.
Jenner usa ese nombre.
Jenner uses that name.
Every time you get a vaccine, you're etymologically getting a little piece of a cow.
I find that oddly charming.
But look, let's talk about what vaccines were actually fighting, because the scale of these diseases is almost impossible to imagine now.
La viruela es muy peligrosa.
Smallpox is very dangerous.
Mata a millones de personas en el mundo.
It kills millions of people around the world.
Smallpox.
We're talking about a disease that killed roughly three hundred million people in the twentieth century alone.
Thirty percent of the people who caught it died.
And the ones who survived were often left blind or with severe scarring.
It shaped the course of history.
It helped destroy indigenous civilizations in the Americas when European colonizers arrived.
This wasn't a minor inconvenience.
Bueno, en 1980, la viruela desaparece completamente.
In 1980, smallpox disappears completely.
Las vacunas la eliminan.
Vaccines eliminate it.
1980.
The World Health Organization declares smallpox officially eradicated.
Gone.
A disease that killed hundreds of millions, simply...
gone.
Because enough people got vaccinated.
I mean, when you think about that as a public health achievement, there's nothing comparable in human history.
La polio también.
Polio too.
La vacuna de la polio cambia todo.
The polio vaccine changes everything.
Polio is personal for a lot of Americans of a certain generation.
My father remembered the fear of summers in the 1950s, when parents wouldn't let children swim in public pools, go to the movies, anything, because polio outbreaks happened every summer.
Kids ended up paralyzed.
And then Jonas Salk announces a vaccine in 1955, and the reaction is, by all accounts, just extraordinary.
La gente llora de alegría.
People cry with joy.
Es un momento muy emotivo.
It is a very emotional moment.
Church bells rang.
Teachers wept in classrooms.
Salk became a national hero overnight.
And interestingly, he refused to patent the vaccine.
Someone asked him who owned the patent and he said, well, the people, I guess.
A decision that, by some estimates, cost him hundreds of millions of dollars.
So now I want to push into something a bit more uncomfortable, because vaccines, despite all of this, are not universally embraced.
Es que algunas personas tienen miedo de las vacunas.
Some people are afraid of vaccines.
No confían en ellas.
They don't trust them.
And I don't think that fear is stupid, or simple to dismiss.
The history of medicine includes real abuses, real cases where marginalized communities were used in experiments without consent.
So when communities that have been historically mistreated express suspicion, that's not ignorance.
That's memory.
La verdad, el miedo es comprensible.
Honestly, the fear is understandable.
Pero la información también es importante.
But information is also important.
Right.
And there's a difference between legitimate skepticism grounded in history, and misinformation, which is the other major driver of vaccine hesitancy.
The 1998 study that claimed a link between the MMR vaccine and autism, which turned out to be completely fraudulent, the data was fabricated, was retracted, the author lost his medical license, and yet the damage it did to public trust has never fully healed.
Bueno, la ciencia dice: las vacunas no causan autismo.
Science is clear: vaccines do not cause autism.
Es muy claro.
This is well established.
Absolutely clear.
Dozens of large-scale studies, millions of children, no link.
Full stop.
But here's what's tricky: once fear takes root, data alone doesn't dislodge it.
People are not calculators.
We process information through stories, through trust, through community.
And that's actually a lesson for scientists and public health officials, not just for the skeptics.
Mira, hay un concepto muy importante.
There is a very important concept.
Se llama inmunidad de grupo.
It's called herd immunity.
Herd immunity.
This is where the individual decision becomes a collective one, which is where it gets ethically interesting.
So, explain it simply for me.
A ver, si muchas personas tienen la vacuna, el virus no puede moverse.
If many people have the vaccine, the virus cannot spread.
No encuentra personas vulnerables.
It finds no vulnerable people.
So the virus runs out of hosts.
It hits a wall.
And crucially, that wall protects the people who cannot get vaccinated, newborns, people with certain immune conditions, cancer patients on chemotherapy.
They're protected not by their own immunity but by everybody else's.
So when someone chooses not to vaccinate, they're not just making a personal health decision.
They're making a decision that affects the most vulnerable people around them.
Exacto.
Exactly.
Necesitamos muchas personas vacunadas.
We need a large majority vaccinated.
Para el ochenta o el noventa por ciento.
Around eighty or ninety percent.
The threshold varies by disease.
Measles, which is incredibly contagious, requires about ninety-five percent vaccination coverage for herd immunity.
Polio is closer to eighty.
The more contagious the disease, the higher the bar.
And look, this is where the COVID-19 vaccines become such a fascinating, and contested, chapter of this story.
La vacuna de COVID usa tecnología nueva.
The COVID vaccine uses new technology.
Se llama ARN mensajero.
It's called messenger RNA.
mRNA.
And this genuinely was new, at least in terms of approved vaccines used at scale, though scientists had been working on the technology for decades.
And I think this is where a lot of people got nervous, understandably so, because everything happened so fast.
Normally vaccine development takes ten, fifteen years.
This happened in under a year.
Bueno, el ARN mensajero enseña a las células.
Messenger RNA instructs cells.
Las células hacen una proteína.
The cells produce a protein.
So instead of introducing a weakened or inactivated version of the virus, which is the traditional approach, mRNA vaccines give your cells instructions to build one specific protein from the virus.
A spike protein in COVID's case.
Your immune system sees that protein, says: that's foreign, that doesn't belong here, and it builds a defense.
And then the mRNA itself breaks down and disappears.
It doesn't touch your DNA.
It never enters the nucleus of the cell.
La verdad, los científicos trabajan muy rápido.
Honestly, scientists work very fast.
Pero el trabajo es serio y riguroso.
But the work is serious and rigorous.
And the speed is actually explainable, not suspicious, when you dig into it.
The trials weren't shortened;
they were run simultaneously rather than sequentially.
Regulators prioritized review.
There was essentially unlimited funding.
And crucially, because COVID was spreading so fast, the trial populations accumulated enough data very quickly.
The shortcuts people feared weren't actually taken.
Though I understand why people needed that explained clearly, because it wasn't always explained clearly.
Mira, la comunicación es muy importante.
Communication is very important.
La gente necesita información clara.
People need clear information.
That, to me, is maybe the most important takeaway from the whole COVID vaccine experience.
The science was sound.
The communication was, in many places, a failure.
And in the vacuum left by poor communication, misinformation flooded in.
That's a lesson that public health institutions are still, honestly, reckoning with.
Las vacunas son uno de los mejores inventos de la historia.
Vaccines are one of the greatest inventions in history.
No hay duda.
There is no doubt.
No doubt at all.
And I think the thing I keep coming back to is scale.
It's hard to grieve for diseases that no longer exist.
Nobody's scared of smallpox.
Nobody lies awake worrying their kid will come home from the swimming pool paralyzed by polio.
And because those fears are gone, it's easy to forget what produced that safety.
These conversations matter.
Knowing how vaccines work, really understanding it, makes you a more informed citizen, a better parent, a better neighbor.
That feels worth two thousand miles of podcast to me.
Bueno, las vacunas protegen a todos.
Vaccines protect everyone.
Es un regalo para la humanidad.
They are a gift to humanity.