What is a vaccine? Why vaccines are important and how long they last

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What is a vaccine? Why vaccines are important and how long they last
Historically, vaccines are one of the most important and effective public health achievements.Johannes Eisele/AFP via Getty Images
  • A vaccine is part of a germ that is exposed to your immune system in a safe way so that it can learn how to fight off that harmful pathogen and protect your body from it in the future.
  • Vaccines are important because they can greatly reduce and prevent the spread of disease — they have even eradicated some life-threatening diseases worldwide.
  • Here are five of the most important vaccines ever, according to public health experts.
  • This article was medically reviewed by Alex Berezow, PhD, a microbiologist at the American Council on Science and Health.

Vaccines are the most effective way to prevent the spread of disease. Because of these immunizations, life-threatening diseases like smallpox have been eradicated worldwide.

"We have so many vaccines that are effective, that we are not seeing vaccine-preventable illnesses like we were in the past," says Joseph Comber, PhD, a biology professor at Villanova University.

For reference, the World Health Organization (WHO) estimates that vaccines stop 2 to 3 million deaths annually. And that's only possible due to the large number of immunizations being administered.

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Here's what you need to know about why vaccines are important, including five of the most significant ones ever developed.

Vaccine basics

A vaccine is a part of a virus or bacteria that is exposed to your body in a safe and effective way. It is often a weakened or dead part of the germ. Then, if you encounter those germs in your day-to-day, the immune system will know precisely how to fight them off.

When a germ or pathogen does enter your body, your immune system quickly recognizes there's an intruder and works to prevent it from spreading. As the immune system embarks on this effort, it makes specialized memory cells that can recall a pathogen or germ.

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"The next time that same pathogen or germ gets into our bodies, the memory cells can respond much more quickly," explains Comber. There's also the benefit of large-scale immunization.

Immunizing the public with vaccines ensures that contagious diseases do not spread, and if they do, that the mortality rate and number of people affected are as minimal as possible.

Vaccines also ensure that high-risk populations — like people with autoimmune disorders, infants, and older people — are shielded from these diseases. This process of protecting those more at risk is called herd immunity. Herd immunity means that most if not all people become immunized in order to protect these more vulnerable populations.

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Are vaccines safe?

In order for vaccines to be released for patient use, they undergo years of development, testing, and vetting to ensure their safety and to avoid any major, long-term complications. This means: yes, they are safe in the wide majority of cases.

Individual vaccines come with their own indicated risks which you can research on the CDC's website under "Vaccine Information Statements."

Moreover, once a vaccine is approved by the FDA and distributed for public use, the CDC along with the FDA and other regulatory agencies monitor them to ensure they don't have significant adverse effects.

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However, vaccines do come with side effects that vary depending on the vaccine. Generally, these side effects are very mild and rarely result in serious complications. Some side effects include:

Vaccine side effects are only serious in rare cases, but certain vaccines may not be right for people with allergies, people who are pregnant, suffer from neurological disorders, or people with a compromised immune system. These are just some of the demographics who may not be able to receive certain vaccines. For a full list, check out the CDC's list of vaccines that may have adverse effects for certain people.

It's always best practice to check with your doctor before you get vaccinated to make sure it's safe for you.

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What are the 4 types of vaccines?

Vaccines are generally made by injecting patients with a mild form of the disease or isolating parts of the disease-causing microbe to familiarize the immune system with how the disease works so it can fight it.

Think of it like getting top secret intel on an enemy before they attack. There are four kinds of vaccines, each protect against certain diseases, but approach preventing infection in different ways.

Why don't vaccines make me sick?

Vaccines introduce a pathogen to your immune system in a form that can't cause sickness. "Without ever being sick, we're educating our immune system on how to remember a germ," Comber says.

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Yes, vaccines do come with side effects. However, these side effects never mirror the symptoms of the disease the vaccine is targeting. Rather, they inject your body with antigens that help your immune system create antibodies that fight off disease.

A common misnomer is that getting a vaccine infects you with a virus or germ. But this isn't true and any side effects resulting from a vaccine (like redness, achiness, or fever) are not because you're infected with the disease.

Insider's takeaway

Vaccines are the first and best way to prevent disease in the population at large. Vaccines distributed to the public help protect against preventable and dangerous diseases.

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Most vaccines have very mild side effects and only have serious adverse effects in rare cases.

Speak to your doctor before getting a vaccine if you have a compromised immune system, are pregnant, or anticipate that a medication or your medical past could interact negatively with a vaccine.

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