How are vaccines made?

How are vaccines made?


How are vaccines made?

Image of a large family sitting around the Thanksgiving dinner table. Mother, at the head of the table, is talking

Mom: I’m so glad we could all be together for Thanksgiving this year! Emily, we are especially happy to finally meet you. Sam has been talking about you non-stop since you started dating.

Image of a young adult male (his son Sam) and his girlfriend (Emily) smiling

Sam: Finally you have a doctor in the family, mom! (laughs) Emily is almost out of medical school. She worked at a vaccine clinic in the city as part of her residency.

Image of mom smiling and talking

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

Image of Dad, sitting at the other end of the table, talking

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

Image of Emily speaking

Emily: I fully understand your concern, Mr. Rose. But much work needs to be done to make sure vaccines are safe and effective. Can I tell you something about what they look like if you’re interested? I don’t want to bore everyone. (laughs)

Image of everyone at the table (except Emily) nodding and smiling

Dad: I’d love to hear an expert source, Emily – and we’ve got a lot of turkeys to get through here! (laughs) Please go ahead.

Step 1: Choosing a goal

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

Immune problems

Too rare

Not serious enough

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

Some viruses are not good targets because of the way they interact with the immune system. Others are too rare or don’t cause disease severe enough to require a vaccine.

Image of a grown woman (Aunt Lucy) talking at the table

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

Image of Emily nodding

HIV with a circle and a slash around it

Emily Exactly. Although scientists are working on an HIV vaccine. HIV is not an easy target.

Phase 2: Exploratory phase

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

Image of a laboratory filled with a diverse group of scientists hunched over microscopes

During this stage, researchers study how the virus or bacteria affects the immune system.

Image of Emily speaking

Visual representation of the process of imitating the invader which teaches the body to fend off viruses/bacteria

The goal is to create a “mimic invader” that teaches our bodies how to fend off viruses or bacteria. This way, our immune system knows what to do when it encounters something real.

Step 3: Preclinical testing

Once the vaccine is finally developed, preclinical testing can begin.

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

During this stage, the vaccine is tested in several ways that don’t involve people.

Image of a syringe/needle with a red X on it

Unfortunately, not many vaccines pass preclinical testing because they don’t activate the immune system as well as they should.

Sam talks as he puts more food on his plate

Sam: If a vaccine shows potential, what happens next?

Step 4: FDA approval for clinical trials

Emily: The next step is to get FDA approval for clinical trials. This happens in three stages.

A diverse group of people lined up to get a vaccine from a woman in a lab coat.

During the first stage of clinical trials, small groups of people receive the experimental vaccine.

A larger, more diverse group of people have lined up to get a vaccine from the same woman in a lab coat

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

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

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

The little boy looks up from eating his meal

Kid: How do they make sure a vaccine works for everyone?

Image of Emily speaking

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

Phase 5: Production and distribution

Vaccines that come off the production tapes and are shipped and then arrive at doctors’ offices, pharmacies, public health centers

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

Image of dad talking

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

Image of checklist with the words “safe” and “effective” ticked

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

Image of dad nodding and talking

Dad: I have to 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)

Image of Emily laughing and talking

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

Image of mom laughing and getting up from the table

Mom: By the way, who wants pumpkin pie?

Image of everyone at the table smiling and raising a hand


Image of dad receiving a vaccine.

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

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

For more information, visit

This resource was created with support from Merck.