How Do Vaccines Work? Here's What You Should Know : Life Kit Just because you (or your kids) are home all day doesn't mean you can skip your vaccines, including a flu shot. Here's how vaccines work and why they're important this year.

Vaccines 101: How They Work And Why You Need Them

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I'm Dr. Mara Gordon, and this is NPR's LIFE KIT.


GORDON: I'm a family physician. And this fall, all my patients are asking me about vaccines. They want to understand what they're hearing in the news about a COVID-19 vaccine. They've got questions about the flu shot. They want to make sure their kids are up to date on their childhood vaccines. Vaccines are on the brain.


GORDON: Our team here at LIFE KIT cannot predict the future of a vaccine for COVID. Nobody can. But we don't want you to forget about all of your regular shots. They could save your life.

MELISSA MARTINEZ: Yeah, I think vaccines are one of the great achievements of mankind. And everybody - the World Health Organization and other experts have said that it's one of the few things that has really helped to decrease morbidity in the world.

GORDON: That's Dr. Melissa Martinez. She's going to answer the most common questions about routine immunizations. Those are the regular vaccines that help keep you and your kids safe. This episode - vaccines 101.


GORDON: Dr. Melissa Martinez is a family physician and a professor at the University of New Mexico.

MARTINEZ: I did some advanced study on immunization with the American Academy of Family Physicians. And I serve on the National Vaccine Advisory Committee, where I'm a co-chair on the subcommittee on Vaccine Equity.

GORDON: Dr. Martinez loves vaccines. But when she was a young mother, she was a skeptic.

MARTINEZ: But I looked at the evidence. I looked at the science behind vaccines, and I realized that by getting my children vaccinated, I was protecting them. But I was also protecting all the other children in their community that they were around, and that their chances of getting ill was really - from the vaccine was really pretty slim, whereas their chances of getting ill from some of these diseases that we protect against is high.

What I tell people - what I tell parents and other people is that we're all just trying to do the right thing, right? We want to do the right thing for our patients. We want to do the right thing for ourselves. So if we can protect against those diseases, let's do it. Vaccines are a gift not only to us but to future generations.


GORDON: Let's start with some basics. How were vaccines discovered? And how do they work?

MARTINEZ: Interestingly, vaccines were actually discovered a long time ago. Back in the 16th century, we think that people in China and other parts of Asia understood that by being exposed to small doses of certain diseases, people would later on develop an immunity that would protect them from getting infected again. So vaccines work like this.


MARTINEZ: Imagine that you've had a disease and you've survived the disease. You may have some immunity. You may have some antibodies and other cells that help you, to protect you from getting sick again, even if you're exposed to the virus or bacteria.

So vaccines mimic that initial disease without getting you sick. Usually, what they inject in a vaccine is a little part of a virus or a bacteria, or a killed virus or bacteria, or one that's been very, very weakened. And that makes the body mount an immune response to generate antibodies and other protective cells so that the next time you're exposed to the real virus, you don't get sick.

GORDON: So your body's kind of prepared to fight it off.

MARTINEZ: That's exactly right.

GORDON: The COVID vaccine is on everybody's minds. And we can't predict what's going to happen with that. But I think people have a lot of questions about how we will know that it's safe and how we'll know that it works - right? - how we know that it's effective. What are you looking for? As somebody who's on the National Vaccine Advisory Committee, what are we looking for with a COVID vaccine to make sure that it's ready for everybody to use?

MARTINEZ: Well, there's a couple of things that you should know about the COVID vaccine. First of all, for people that develop vaccines, this isn't their first rodeo. There have been other infections with viruses that are like COVID, coronaviruses like SARS and MERS. And people started to develop vaccines against those viruses. So when the coronavirus - the new coronavirus, the one that causes COVID-19 - came out, they were ready to start developing a vaccine. And that's one reason that the vaccine has gone so rapidly. Another reason is that a lot of people are collaborating and working together. And a third reason is that there's really some new technology out there that we've never had before that has enabled the vaccines to be manufactured much more quickly.

That being said, even a vaccine that's manufactured quickly has to go through extensive testing. First of all, is it safe? Does anybody have an adverse reaction? And second of all, is it effective? And they'll monitor people for a long time and see if people who got the vaccine do better than people that didn't get the vaccine. And if there's any safety signal, they'll act on it.

In addition to that, every vaccine that's approved has to be approved by the FDA, not only in terms of how the vaccine is made but what additives are put into it and how it's manufactured. Then, it has to go to the Advisory Committee on Immunization Practices, and they have to look at the evidence and safety. So there are a lot of safeguards in place.


GORDON: Thank you. That's super helpful. And so everybody's thinking about the COVID vaccine. But people should also still be getting their routine immunizations, all those normal shots that we get every year, that kids get, that older people get. Should we be making any changes to how we think about getting our routine shots in the context of the COVID-19 pandemic?

MARTINEZ: Great question. And it's incredibly worrisome that people are not getting their routine vaccines, especially children. And I understand the reason for that. Nobody wants to go to a doctor and be in a crowded waiting room during this time. But recognizing that the rate of immunizations has gone way, way down, physicians across the country have taken measures to be able to get people to be immunized in a manner that is safe and effective. Some practices will actually go out and see people in their cars. I know at my institution, we're offering drive-through flu shot vaccines.

But it's imperative that people, and especially children, get their vaccines. Last year, we had a terrible, terrible year with measles where a lot of people got sick. And we were really afraid that measles was going to spread all over the country and we were going to have a big problem with a disease that people don't realize is very, very serious and can often cause death. So we don't need another outbreak on top of COVID. So it's really important that people get their routine vaccines.

GORDON: So I love that example of the drive-through flu shots that you're doing in your practice, Dr. Martinez. What are some other questions that people can ask their doctor or ask their pharmacy about how to keep them safe when they come in for their regular shots?

MARTINEZ: Sure. It's a good idea to call your pharmacy, or physician, or even your public health office if that's where you're going to go to get your shots and ask them what they're doing. And a lot of times, they're staggering appointments. They're making sure everybody wears masks. They're wearing extra protective equipment. And they have a flow process so that people pass through the clinic in a way such that they don't interact with people. There's also a lot of extra cleaning and other measures going on to ensure that people who come to clinic to get protected against one disease don't contract another.

GORDON: That brings up a trend I've been seeing in my own practice as a family physician. We're seeing a really worrisome decline in well-child visits since school-age kids, they often come in for the back-to-school physical where, you know, we make sure they're healthy for school, and they get all their shots.

So first of all, to our listeners, your kid's doctor would love to see your kids. And if you have concerns about bringing them in, please give the office a call and talk them through. But if kids' well-child checkups have been delayed, Dr. Martinez, how can families keep track of what vaccines their kids need and make sure that they're up to date?

MARTINEZ: Sure. There's a lot of different ways. One way is that most states have something called the immunization information system, which actually tracks vaccines on a statewide basis. And you can contact your health department to see if you can get that report. A lot of schools and doctors' offices are - actually have access to that and are able to generate those kind of reports for you. Another thing parents can do is just keep track of their handheld immunization reports. And yet another thing is there's an app on the CDC where you can look and see what vaccines might be required for your child. Are you depending on your age group and conditions?


GORDON: Let's talk about the flu shot. It's on a lot of people's minds. Why is it extra important this year?

MARTINEZ: Oh, the flu shots are incredibly important this year. What we know is that a lot of people every year die from the flu. So we already have a great deal of deaths occurring with COVID. And we don't need flu deaths on top of that. What we know from studies that came out of Wuhan is that some people contracted both COVID and the flu, and those people did not survive. They did not do very well.

In addition to that, if there's a lot of flu in a community and a lot of COVID in a community, emergency rooms and hospitals could easily be overwhelmed. And so we need to keep people well and out of hospitals so that the hospitals can do what they need to do when people are sick with diseases that they can't avoid.

GORDON: Why do you need a flu shot every year?

MARTINEZ: So our ability to stay immune to flu changes because the virus changes slightly every year. And until we figure out how to give people a flu shot that makes them immune for life, we have to change people's immunity with a booster flu shot, a new flu shot every year.

GORDON: And what's the best time of year to get the flu shot to prevent symptoms and make sure that you're immune throughout the flu season?

MARTINEZ: Usually, we say late fall. This year, we're really trying to get everybody immunized in October so that when the new COVID vaccines come out, we'll be able to start focusing on COVID vaccines.

GORDON: My patients always have a lot of questions about vaccines and pregnancy and vaccines for older people. These are two groups that we know need to be extra careful about making sure they're up to date on their immunizations because their immune systems aren't as strong. Maybe, we can start with pregnant people. What vaccines should they definitely get? And what vaccine should pregnant people avoid?

MARTINEZ: We know for sure that every pregnant woman should get a flu shot because if a pregnant woman gets flu, she's a lot more likely to get severely ill. We also think that every pregnant woman, during her third trimester, should get the pertussis vaccine, which helps to protect her baby until her baby's old enough to get its own vaccines and develop its own immunity. And in both - with both of those vaccines, it's proven that there is a better pregnancy outcome.

GORDON: And what's pertussis?

MARTINEZ: Pertussis is whooping cough. And if a newborn baby gets whooping cough, they're very likely to get severely ill, have to be hospitalized. And unfortunately, babies die every year from whooping cough. Vaccines that need to be avoided during pregnancy are vaccines that are made by weakening a virus. So we call it attenuated vaccines. So vaccines like polio and mumps, measles and rubella should be avoided during pregnancy.

GORDON: Let's talk about older adults now, another common group that we, as primary care doctors, really try to focus in on and help make sure that our patients get vaccinated. What vaccines should older adults really focus on, making sure that they're getting?

MARTINEZ: OK. So there are two vaccines available. For most people over 65, they should probably get both vaccines. They protect against invasive pneumococcal disease. They protect against life-threatening diseases called meningitis, which is an infection in the nervous system. And they protect against sepsis or an infection in the bloodstream. Adults should get a shingles vaccine. And all adults over - well, everybody age 6 months and up should get a flu shot. And then if people haven't received a tetanus, diphtheria and tetanus vaccine in the last 10 years, they should get that as well.

GORDON: Let's talk about side effects of vaccines. That's a really common question that comes up. What side effects are myth? And what side effects are reality?

MARTINEZ: Well, I have a hard time talking about myths because it's kind of like playing whack-a-mole...


MARTINEZ: ...When one myth pops up, and you kind of knock it down. And then suddenly, there's another myth or misconception. Vaccines do not cause autism. Vaccines do not cause brain damage or other problems. In terms of side effects, almost all vaccines cause a little bit of a problem because people who get the vaccines, their body is responding, their immune system is acting up. So people who get the vaccines are likely to get a sore arm. They're likely to get a little bit - maybe a low-grade fever, maybe feel achy for a day or so. But these are pretty minimal. There are very, very rare, serious adverse effects with vaccines. But these are incredibly rare. And in medicine, we look at the statistics. And when we see that a lot of people do really, really well with the vaccine and that the vaccine prevents diseases that can cause them problems, and very, very few people have adverse events, then we tend to recommend those vaccines.

GORDON: What do you tell your patients who say, hey, Dr. Martinez, I'm not going to get the flu shot because last year, I got it and I swear, I got the flu. I felt so sick after I got it.

MARTINEZ: (Laughter) I - you know, I get that. I hear that all the time. And I think the flu shot can make some people feel really, really cruddy. And I understand that. But getting the flu would make people feel so much worse. I think people can take some ibuprofen and get through the - not feeling so good with the flu shot and still be protected.

GORDON: Are there people for whom their immunity might have waned from their childhood vaccines? And how would they know?

MARTINEZ: Absolutely. And we see that a lot. And we don't always routinely check to see. I know health care workers, when they start working in the health care field, we check them for mumps, measles and rubella antibodies to see if they're immune. Or if there's an outbreak, we'll check for those kind of - the waning of immunity so we can assess antibodies. It's not the - antibodies doesn't give us the full story, but it gives us an idea whether or not somebody's immune system might be effective in fighting off the disease.

GORDON: Yeah, thank you. That's helpful. A final question for you. I think about this a lot in my own primary care practice that it feels like we're in this moment where there's a lot of lack of trust in public health institutions and in medical institutions. So as somebody with a public role in promoting vaccines, how do you think our public health organizations can win back people's trust?


MARTINEZ: I think that trust needs to be developed in a one-on-one setting. I think that practices need to practice culturally effective care by listening to people and staying naturally curious, and making sure that you have translators when appropriate, and really thinking about people as individuals. I think organizations need to be open and honest about the true side effects and consequences and understanding the risks and benefits. And hopefully with time, we can rebuild the vaccine infrastructure that has kept us protected for all these years.

GORDON: I hope so.


GORDON: Thanks, again, to Dr. Melissa Martinez for talking with us.


GORDON: For more LIFE KIT, check out our other episodes. We've got an episode on how to make the most of your telehealth appointment, another on how to start therapy and lots more. You can find those at And if you love LIFE KIT and you want more, subscribe to our newsletter at And as always, here's a completely random tip, this time from listener Ashley Hoffman (ph).

ASHLEY HOFFMAN: Hi, NPR. I have some advice for all the parents out there who are finding themselves juggling kids at home. What I have found that's been really successful is I have repurposed all the rooms in my house. So what would've been a really cute little reading area is now art center. And where I would've had a trunk with a cute blanket is now Hot Wheels village. I feel like no matter how big or small your house is right now, it's still possible to make a destination in a different part of the house. So I hope that's helpful. Thank you.

GORDON: Do you have a random tip? Leave us a voicemail at 202-216-9823, or you can email us at This episode was produced by Andee Tagle. Meghan Keane is the managing producer, and Beth Donovan is our senior editor. Our digital editor is Clare Lombardo, and our editorial assistant is Clare Marie Schneider. I'm Mara Gordon. Thanks for listening.

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