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What are vaccines and how do they protect you?

Jessica Hess COVID-19 Science Viruses

What is a vaccine?

Some diseases are more difficult to prevent than others, so although good personal and public hygiene can help slow the spread of germs, they aren't 100% effective.

Vaccines are made using a weakened, dead, or partial form of a disease-causing bacteria, virus, or parasite. In their weakened state, the germ is unable to replicate quickly enough to make us sick. Instead, they protect us from the pathogen they're made from by introducing our immune system to a smaller, inactivated portion of the germ. Inside our body, vaccines trigger a reaction from our immune system which orchestrates the production of proteins (antibodies) capable of quickly attaching to and immobilizing live germ particles if they're encountered.


Types of vaccines

1. Live, attenuated vaccines are designed to target viruses and bacteria. A weakened version of the pathogen is used to make the vaccine. They're as close to a natural infection as you can get.

Ex. Mumps, Measles, Chickenpox vaccines

2. Inactivated vaccines also target viruses and bacteria, but in this type, a dead form of the pathogen is used to make the vaccine. Booster doses of inactivated vaccines are often necessary for sufficient immunity.

Ex. Polio vaccine

3. Subunit vaccines are also virus and bacteria fighters, but they contain only essential pathogen parts in the vaccine, reducing the risk of side effects.

Ex. Pertussis vaccine

4. Toxoid vaccines are designed to target toxin-producing bacteria. A weakened form of the toxin, called a toxoid, is used to make the vaccine.

Ex. Tetanus, Diphtheria vaccines

5. Conjugate vaccines are targeted against bacteria with a polysaccharide (sugar) coating. These bacteria are sneaky and can go unnoticed by the immune system. This type of vaccine attaches specific parts of the pathogen to the coating, making it visible to our immune cells.

Ex. Haemophilus influenzae type B (Hib) vaccine


[ Click here for the CDC's complete list of vaccinations ]


When should I get vaccinated?

Child & Adolescent Immunization Schedule (CDC, 2020)


Adult Immunization Schedule (CDC, 2020)


How vaccination works — a scenario

Disclaimer: I recommend reading this section ignoring the words in parentheses first, then reading once more to get an understanding of how this scenario is similar to what happens in your body after you've been vaccinated.


Think of getting a vaccine as providing your body's police force (immune system) a sketch that shows a distinct birthmark (vaccine) belonging to a suspect (pathogen) that has been breaking into houses in your neighborhood (making people sick). News travels pretty fast around the police station, but it still takes a few weeks for every officer to see the sketch, so you'll have to be cautious because the suspect is still out there. You aren't protected (immune) yet.

BUT! If you manage to stay safe those first few weeks, every officer will know what the suspect looks like and can readily identify, call for backup (make antibodies), and arrest them (provide immunity) if they're ever seen on your property.


TL;DR Vaccines teach your body to recognize a key component of a disease-causing germ. This allows your immune cells to recognize the germ faster and kill it more efficiently if you were to become infected.


How are vaccines made?

Watch the video below for a great 5-minute explanation of Sanofi's process!


Are vaccines safe?

Vaccines are extensively tested in the lab before they are ever used by a human. The FDA uses the results of these lab tests to determine if a vaccine candidate is suitable for a clinical trial.

Clinical trials often start with 20 to 100 volunteers that agree to get vaccinated, and end with 1000s of participants. The following safety concerns must be addressed in the trial:

  • If the vaccine is safe
  • What dosage works best
  • How the immune system reacts to it

Once approved for clinical use, the company that makes the vaccine continues to conduct laboratory tests to guarantee the quality, potency, and sterility of each batch. The FDA, CDC, and other agencies regularly monitor the results of these lab tests (and inspect the vaccine factories) to ensure quality and safety standards are being met.

The first time your body encounters a pathogen, it takes several days for your cells to learn how to make the specific antibodies needed to fight the disease. The second time around, your cells already know what antibodies to make — so they can neutralize the germ faster. Vaccines are safer than acquiring natural immunity because the vaccine trains your immune system for the first time using an inactivated look-alike instead of the live pathogen.

The reason you may feel feverish after an immunization isn't because it made you sick, it's because your immune cells are hard at work creating antibodies custom fit for the germ!

Did you know that getting vaccinated can protect people around you from getting sick too?

For at-risk populations, like babies and people with weakened immune systems (HIV, cancer), certain vaccines can trigger an abnormal and potentially harmful reaction.

Herd immunity is when vulnerable members of a group are protected from a disease because most of their community has developed immunity. Vaccines make it a lot harder for diseases to spread from person to person, thereby protecting those in your community that cannot (or choose not to) be immunized.


How long does immunity last?

Some vaccines offer lifetime immunity with just one shot, but others require boosters or annual shots to keep you protected. To see what vaccines you may be due for, take the CDC's quiz below! (or click here to be directed to the full website)



I hope you enjoyed this introductory lesson on how and why vaccines work! Consider saving this post (and the references linked below) to look back at the next time you are offered a vaccine.

For most people, the rewards of vaccination greatly outweigh the risks, but ultimately the choice is yours. I'm here to help you think like a scientist  keep an open mind, gather data, consider all options, and use your knowledge to make the best possible decision for your health and those around you.





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  • Dyanna on

    This article answers all the questions I’ve had about vaccines . I’ve stopped getting vaccines but ever since this pandemic it’s opened my eyes to the need to take them .

  • Guadalupe Faz on

    Very good information about getting vaccinated, but it’s something to think about.

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