How are Vaccines Made?

how are vaccines made video still

How Are Vaccines Made?


Mom: I’m so glad we could all be together for Thanksgiving this year! Emily, we’re especially glad to finally meet you. Sam has been gushing about you nonstop since you two started dating.

Sam: You finally have a doctor in the family, Mom! [laughs] Emily is almost done with med school. She’s been working at a vaccine clinic in the city as part of her residency.

Mom: How wonderful! I just got my flu shot last week. I just wish I could convince Sam’s dad to do the same.

Dad: I’m sure you’re doing good work, Emily. I’m just not convinced that vaccines are safe. How do they even come up with those things?

Emily: I totally understand your concern, Mr. Rose. But a lot of work goes into making sure vaccines are safe and effective. I can tell you a little bit about how they’re made if you’re interested? I don’t want to bore everyone. [laughs]

Dad: I’d love to hear from an expert source, Emily — and we’ve got a lot of turkey to get through here! [laughs] Please, go ahead.

Step 1: Choosing a Target

Emily: Well, first, scientists choose which illness-causing virus or bacteria to target with a vaccine.

Immune issues

Too rare

Not serious enough

(these words should come in one at a time to match VO)

Some viruses aren’t good targets because of the way they interact with the immune system. Others are too rare, or don’t cause sickness serious enough to need a vaccine. 

Aunt Lucy: Is that why there’s no vaccine for HIV? Because of the way it affects the immune system?

HIV with a circle and slash around it

Emily Exactly. Although scientists are working on an HIV vaccine. HIV just isn’t an easy target.

Step 2: Exploratory Phase

Once a vaccine target has been chosen, the exploratory phase begins. 

During this phase, researchers study the way the virus or bacteria affects the immune system.

Visual representation of the process of the imitation invader teaching body to fend off virus/bacteria

The goal is to create an “imitation invader” that teaches our bodies how to fend off the virus or bacteria. That way, our immune system knows what to do when it comes across the real thing.

Step 3: Pre-Clinical Testing 

Once the vaccine is finally developed, pre-clinical testing can start. 

Series of images: first a Petri dish, then a math equation, then a white mouse 

During this phase, the vaccine is tested in a few different ways that don’t involve people.

Unfortunately, not many vaccines make it past pre-clinical testing because they don’t activate the immune system the way they should.

Sam speaks while he puts more food on his plate


Sam: If a vaccine does show potential, what happens next? 

Step 4: FDA Approval for Clinical Testing

Emily: The next step is getting approval for clinical testing from the FDA. This happens in three phases.


A diverse group of people lined up to get a vaccine from a lab-coated woman.

During the first phase of clinical testing, small groups of people receive the trial vaccine.

A larger, diverse group of people lined up to get a vaccine from the same lab-coated woman

During the second phase, the study is expanded to include people who share things in common (like age and health) with the people the vaccine is intended for.

An even larger diverse group of people lined up to get a vaccine from the same lab-coated woman

During the third phase, the vaccine is given to thousands of people to make sure it’s safe and effective.

Little boy looks up from eating his meal 

Little Boy: How do they make sure a vaccine will work for everyone? 

Emily: Well, clinical trials try to include a lot of different types of people to make sure the vaccine works well for everyone, without dangerous side effects. 

Step 5: Production and distribution

Vaccines coming off manufacturing belts and being shipped to and then arriving at doctor’s offices, pharmacies, public health clines 

Once a vaccine is finally approved, that’s when it gets mass-produced and distributed to doctor’s offices, pharmacies and public health clinics across the country. 

Dad: That’s the part that worries me. How do we know a vaccine is safe when it’s never been used before?

Emily: I hear you, and I think it’s natural to worry about something brand new. But vaccines are based on years and years of research, and a vaccine is never approved by the FDA unless it’s proven to be safe and effective.

Dad: I must say, you’ve made a convincing case for vaccines, Emily. I have to confess, I didn’t know half of what you just told us. [laughs]

Emily : Most people don’t! And there’s a lot of misinformation about vaccines out there. That’s why I’m always willing to talk about them — at least until it’s time for dessert … 

Mom: Speaking of which, who wants pumpkin pie?

Want to make sure you and your loved ones are up to date on vaccines? Your healthcare provider, pharmacist or local health department can help.


You can also visit the CDC website to learn more about vaccines and vaccine schedules.

For more information, please visit

This resource was created with support from Merck.

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