If Your Vaccine Works, Why Do You Care If I Get One?
My vaccinated kids are protected. But “protected” and “invincible” aren’t the same thing.
Is my vaccinated kid protected against X, Y, Z...? We’re getting some version of this question constantly right now. Parents see headlines about declining vaccination rates and measles outbreaks in 24 states, and they want to know: are my kids okay? I’d be lying if I said I hadn’t wondered the same about my own children.
The short answer is yes. Two doses of MMR are about 97% effective at preventing measles, and real-world data from recent outbreaks suggest we may be underestimating that figure.
And to pre-empt the follow-up question we get from parents of kiddos too young for their second dose: even one dose is quite effective, around 93%. Fun fact that most people don’t realize: the second dose isn’t actually a “booster” in the way people use that word. The first dose does the heavy lifting. The second dose exists mainly because about 5-7% of kids don’t mount a full immune response to the first vaccine dose, and there’s no easy way to know which kids those are without drawing blood and running lab tests. So we give everyone a second dose to catch the kiddos for whom the first dose didn’t result in a strong immune response, and to give another opportunity to kids who may not have gotten the first one at all. That means a vaccinated child who comes into contact with someone infected with measles “out in the wild” — on a bus, at a birthday party, wherever — has very, very good odds of not getting sick despite the exposure.
(Quick note for parents of babies: Infants younger than 6 months are generally protected by antibodies from mom, passed through the placenta during pregnancy. This is one of the reasons the childhood vaccine schedule is designed the way it is — the timing isn’t random. It’s built around the window when maternal protection starts to fade, and the baby’s own immune system is ready to take over. If you’re in an active outbreak area, kids as young as 6 months can get an early dose of MMR, but that dose won’t count toward their routine series. They’ll still need their regular two doses starting at 12 months — to ensure a strong immune response — but it can provide real protection during a surge. Talk to your pediatrician!
And for the parents and adults reading this who aren’t sure about their own vaccine status: you don’t need to bother with titers. Antibody levels only tell part of the immunity story — they don’t capture the cellular immunity that also plays a role in protection. If you’re unsure, just get a dose. There’s no harm in getting MMR if you’re already immune, and it’s a lot simpler than trying to interpret a blood test that may not give you the full picture.
Okay, sorry for the detour. Those impressive effectiveness estimates have held up across decades of data and millions of kids. If your child is fully vaccinated, they have strong individual protection. But you already know I love nuance, and we’ll get to the longer answer in a sec — it’s especially important in light of the other question we get all the time: Well, if the vaccine works so well, why should I care whether other people get vaccinated?
I bet you already know what I’m going to say next... Herd immunity. Community protection. Yes, we know you’ve heard it. For a lot of people, that phrase just slides right off the brain at this point. And if you’re someone who isn’t moved by the idea that health is a group project, hearing “herd immunity” one more time probably won’t do it. But we’re gonna give it the ol’ college try...
Let’s try to think about this differently. Because that question — if your vaccine works, why do you care if I get one? — contains a misunderstanding about how vaccines actually function in the real world that’s worth digging into. Let’s discuss…
Your vaccine doesn’t work in a vacuum
Most people think of a vaccine like a force field. You get the shot, you’re wrapped in an invisible bubble, and nothing can touch you. Two doses, 97% effective, done.
But that’s not how it works. A vaccine is more like a really good lock on your front door. If you live on a quiet street, that lock does its job beautifully. Almost nobody’s trying your door, and on the rare occasion someone does, the lock holds.
Now imagine your street gets a lot more foot traffic. Then more. Then it becomes a crowded thoroughfare with people constantly rattling every doorknob they pass. Your lock is still the same lock. It’s still a good lock. But the sheer volume of attempts changes the math. Every exposure is another test of that protection.
This is what’s happening right now in communities where vaccination rates are dropping. And it’s not just about measles. MMR coverage for kindergartners has fallen from 95.2% during the 2019-2020 school year to 92.5% in 2024-2025 (which is below the threshold needed to provide herd immunity). Pertussis (whooping cough) saw major outbreaks in 2025 and continues to circulate. Polio has resurfaced in wastewater in multiple states. These are all vintage diseases we’d gotten so good at controlling that most parents (and even some physicians!) had never even seen a case. That’s changing.
For a virus as contagious as measles (the most infectious disease we are aware of…), which can infect up to 9 out of 10 unvaccinated people who are exposed — even small drops in coverage change the landscape fast. At 95% coverage, there’s very little virus circulating. Your vaccinated child rarely encounters measles at all. Below that threshold, the virus finds gaps. It moves. It circulates longer and reaches more people. And every encounter is another roll of the dice for everyone, including the vaccinated.
What 97% actually means (and doesn’t mean)
That 97% number gets misunderstood a lot, so let’s break it down.
Ninety-seven percent effectiveness doesn’t mean your child has a permanent 97% shield against measles forever. It means that in the populations studied, two doses of MMR prevented measles in about 97% of vaccinated people. Which is incredible. But there are a few wrinkles:
About 3 out of every 100 fully vaccinated people who are exposed to measles can still get infected. That’s called a breakthrough infection. In an environment where measles is rare, this almost never happens because you’re almost never exposed. In an environment where measles is everywhere, that 3% starts to matter more — not because the vaccine got worse, but because the opportunities for exposure skyrocketed.
Vaccine-induced immunity can slowly fade. A Lancet study from 2024 looking at measles dynamics in England found that immunity from the MMR vaccine wanes very slowly — on the order of fractions of a percent per year — but over decades, this means breakthrough infections become more common, especially in people 15 and older. When measles was rare this barely mattered, but when measles starts circulating again it could become relevant.
But even when breakthroughs happen, vaccinated people tend to get milder cases, with lower viral loads and fewer complications. The vaccine - and the immunity it’s built - is still doing work even when it doesn’t fully block infection.
Immune amnesia
We’ve covered this before, but it matters here, so bear with me.
Measles doesn’t just make you sick. It can wipe out your immune system’s memory of other diseases you’ve already fought off or been vaccinated against.
This is called immune amnesia. A 2019 study published in Science looked at unvaccinated children who got measles and found that afterward, they’d lost, on average, about 20% of their existing antibody repertoire. Some kids lost more than 70% of their protection against viruses they’d previously been immune to.
And this happens to virtually everyone who gets measles, even mild cases.
Sit with that for a second. Your child catches the flu at age 3, fights it off, builds immunity. Gets a cold, fights that off too. Over the years, their immune system builds up this whole library of memory from every infection they’ve encountered. Then measles rolls through and just... wipes it, burns down the library. All that hard-won protection against flu, against other infections they’d already beaten, are degraded or gone. And it can take two to three years for the immune system to rebuild. Before the measles vaccine existed, measles infections could be linked to up to half of all childhood deaths from infectious diseases — not from measles itself, but from the immune destruction it left behind.
The MMR vaccine prevents this. Not just measles — it prevents the immune amnesia that measles causes. It protects the entire library, not just one book.
What this means for your vaccinated kid
So. Is your vaccinated child protected? Yes, very likely. And even a breakthrough infection would almost certainly be milder than what an unvaccinated child goes through.
What we can’t tell you is exactly how well that holds up when there’s more virus circulating than we’ve seen in over 30 years. Over 1,000 measles cases across 24 states so far in 2026, and it’s only mid-February. South Carolina alone has over 900 cases — surpassing the Texas outbreak that made national news last year. The U.S. is at risk of losing its measles elimination status, which it has held since 2000. We are in unfamiliar territory.
That 97% effectiveness was established when herd immunity was doing a lot of the heavy lifting. We’re about to find out what happens when you remove that safety net — not just for the unvaccinated, but for everyone.
Why I care if you get vaccinated
So when someone asks me, if your vaccine works, why do you care if I get one? The response is a hodgepodge of these key points:
Because vaccines don’t work in isolation. They work best when most people around you are also protected. The fewer vaccinated people in your kid’s school, their soccer league, their birthday parties, the harder their immune system has to work, and the more often it gets tested.
Because some kids can’t be vaccinated. Babies under a year. Kids on chemo. Children with immune conditions. They’re completely dependent on the rest of us keeping this virus out of their orbit. Can we all agree that infants are worth protecting?
Because even vaccinated people can have breakthrough infections, and the more virus circulating, the more often that 3% chance gets tested.
Because the outcome of measles isn’t just “you get sick and recover” or “you die.” There’s a whole spectrum of damage in between that doesn’t get talked about enough. Immune amnesia can strip away years of built-up immune protection. Subacute sclerosing panencephalitis (SSPE) is a rare but fatal brain disease that can surface years after a measles infection — most commonly in kids who were infected as babies. Hearing loss, pneumonia, and hospitalization. These risks are measured and documented, and some don’t show up until long after the rash is gone.
And because we functionally eliminated this disease, and watching it come back when we have every tool we need to stop it is just... gut-wrenching and wholly unnecessary.
One more thing. Elizabeth Bruenig recently published an essay in The Atlantic called “This Is How a Child Dies of Measles.” She wrote the entire thing in second person — you are the parent, your child is the one getting sick — and it’s one of the most effective pieces of science-adjacent writing I’ve read in a long time. It doesn’t lecture. It just walks you through what actually happens, decision by decision, symptom by symptom, from a birthday party to the ICU. Most of us read something like that and think that wouldn’t be my family. And for vaccinated families, the odds are very much in your favor. But the whole point of this piece is that those odds don’t exist in a vacuum. They depend on what’s happening around you. And what’s happening around us right now is shifting in ways we haven’t seen in a generation.
The bottom line
If your kids are vaccinated, take a breath. They have strong protection. Don’t panic.
But do understand that their protection works best when the people around them are also protected. Unfortunately, that layer is thinning. And it’s worth talking to other parents, gently, about why this was never just a personal choice.
We got here because of collective action. We stay here the same way.
Stay Curious,
Unbiased Science
 | A guest post by
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 | A guest post by
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I’ve been a Critical Care RN for 34 years and I’m exposed to almost everything. I also have been vaccinated for everything possible/available yearly. I also am not afraid to wear a mask when in public during flu season. I can’t remember the last time I’ve had the flu and I have never had COVID and that means something when I’m a Medical ICU NURSE. That’s the ICU where all those pts go when really sick critically. I get the flu and Covid vaccine every year. These vaccines are safe, ongoing research needs to be done. These vaccines can change for the better.
Very important piece, especially coming off the FDAs refusal to review Moderna’s application for a new MRNA based flu vaccine (an unprecedented one). Thank you for your work!