Good to Know: How Vaccines Work (and What Safety Really Means)
Insights From Diana M. Colleluori, PhD, MBA
Vaccine safety is one of those topics where everyone seems to have an opinion, but actual expertise often gets drowned out by noise. Between social media debates and conflicting headlines, it's hard to know what's actually true.
This complex, high-stakes issue felt ripe for the Good to Know treatment. In this series, the Oxford & Em team chats with folks who know a topic inside and out, asking the right questions and turning that conversation into something clear and helpful (albeit high-level).
Luckily, we know someone with incredible insights into vaccines: Diana M. Colleluori, PhD, MBA.
Diana has spent over 20 years helping pharmaceutical and biotech companies bring new vaccines and medicines from the lab to real-world use, navigating all the rigorous steps that happen in between. She's exactly the voice you want when you're tired of sound bites and spin and just want clear answers.
When we asked Diana the big question — Are vaccines safe? — she walked us through the reality: vaccines are among the safest medical tools we have, and that's by careful design.
First: How Do Vaccines Actually Work?
If your last biology class was a while ago, you're not alone. That’s why we started by asking Diana to break down vaccine science in plain English.
"In general, (vaccines) all work the same way," Diana told us. "They stimulate your own immune system to respond against whatever the vaccine is intended for."
Your immune system is always looking out for threats like viruses, bacteria, and things that don't belong. When you get sick, your body learns how to fight back and saves the directions for next time.
A vaccine does this teaching ahead of time, without making you sick. Some vaccines give you a tiny, harmless piece of the actual virus (or a weakened version). Newer mRNA vaccines like the COVID-19 shots just deliver instructions. "The mRNA vaccines basically give you the nucleotide sequence for your body to make the antigen itself," Diana explained. They teach your immune system how to identify the invader, destroy it, and create memory cells to guard you later. And importantly, "the mRNA is degraded by your body," Diana said. "It's not hanging around. It does what it's supposed to do, then it's gone."
From Lab to Approval
It's one thing to know what vaccines do, but how do we know they're safe? Diana walked us through the long path from the lab to the pharmacy shelf.
First comes discovery — figuring out which part of a virus or bacteria makes the best target. Then, researchers do preclinical testing in labs and on animals.
Next come the clinical trials in humans, and this is where the timeline really stretches. Diana explained that, from start to finish, a vaccine typically takes about 10 years to reach approval. The early phases test safety in small groups. Then, bigger phases test both safety and how well it works.
"Phase 1 and Phase 2 are all about safety," Diana said. "Then Phase 3 confirms it works and that it's still safe in a much bigger group."
After that, the data goes to regulators like the FDA — outside, impartial experts who review the results line by line. And here's what many people miss: approval isn't the end. "The evaluation of the safety and effectiveness continues for the life of the drug," Diana said.
In other words, we watch what happens in the real world, in millions of people, and if there's an unexpected side effect, we catch it, study it, and adjust if needed.
Safe Doesn't Mean Risk-Free
Diana was clear: "Nothing you put in your body is 100% risk-free." And vaccines are different from many medicines because they're given to healthy people, so the tolerance for risk is tiny.
The mild side effects (sore arms, slight fevers) are just your body's defense system kicking in. "Your body is mounting a reaction and building up immunity," Diana said. "It might not feel great for a day, but it's preparing to go to war."
Serious side effects? They're very rare. And they're exactly what post-approval monitoring is designed to detect, so you hear about them quickly if they do happen.
Why Boosters Matter
So why do we sometimes need boosters or yearly shots? Diana explained that it comes down to how viruses change and how our immune memory sometimes needs a reminder.
Certain viruses, like flu and COVID, mutate regularly. That means last year's immune memory might not fully match this year's virus version. Boosters update your body's playbook with new instructions, so your defense system stays ready.
They're not just repeats; they're a practical refresh, fine-tuned to tackle new strains. That's why many health experts say it's wise to get flu and COVID shots at the same time. The timing protects you when you're most likely to be exposed to the latest versions.
On Autism and What the Data Really Says
Few myths have been as persistent (and as thoroughly debunked) as the one linking vaccines to autism. Diana didn't mince words: "There is absolutely no link between receiving a vaccine and developing autism spectrum disorder."
She pointed out that safety is studied not just in small trials but forever. We have decades of data, millions of people, and multiple major studies, and there has never been a credible link found between the active ingredients or any of the inactive ingredients and autism.
If that ever changed? The global monitoring system is designed to catch it. But decades in, nothing credible has emerged.
Vaccines, old and new, help us live longer, healthier lives. They're why we don't see smallpox, polio, or measles like our grandparents did. And they're safer now than ever before. Yes, there has been an uptick in autism diagnoses, but that is because we're better at detecting it and have expanded its definition. It's right there in the term; now autism is a spectrum, whereas years ago its diagnosis was limited.
What came through most clearly in our conversation with Diana wasn't just the science, it was also the rigor. Vaccines go through more testing, more monitoring, and more oversight than almost any other medical intervention. They're held to an incredibly high standard precisely because they're given to healthy people, including children.
That doesn't mean they're perfect or risk-free. But it does mean that when Diana says they're among the safest tools in medicine, that assessment is backed by decades of data from millions of people worldwide.
Diana put it best: "Even if you don't believe in science, it's still true."
The Story Behind the Story
We didn't write this because we're vaccine experts.
We're not. (That's the point.)
Our job isn't to be the expert on every topic we tackle. It's to find someone who is, ask the questions that matter, follow the rabbit holes, and translate the answers into something clear, accurate, and useful.
When we're hired to write about complex topics like access control technology for property developers, investing for police officers, or legal rights for people who've never spoken to a lawyer, we start from a place of curiosity. We get up to speed fast. We look for what's missing. We pull on threads. We ask the "dumb" questions so our readers don't have to and come back with a story that's interesting and actionable.
That's the kind of clarity we aim to bring to every subject, no matter how complex, technical, or sensitive. No agenda. No jargon. Just the story that helps people understand.
Want to see how we do it behind the scenes? Read The Art of the SME Interview, our take on what it really takes to ask better questions, and turn expertise into impact.
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