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How Vaccines Work

When people get sick, the immune system usually responds by making antibodies. However, it takes time to make antibodies, which leaves time for the pathogen to cause disease. If you have gotten a disease before, you already have antibodies to it, so the immune system can fight it off quickly.

Vaccines allow people to create antibodies to a disease without getting sick, so if they are exposed in the future they already have antibodies. 

Although no vaccine is perfect and some people will still get infected, people who are vaccinated often have milder symptoms than unvaccinated people. The reason for this is that the immune system has seen the pathogen before, so even if you are not immune, it can fight off the pathogen more easily.

For more information about the immune system, click here. 

Vaccine Schedules

Click Here to Find Your Country's Vaccine Schedule


Schedules for Some Specific Countries/Regions:

Australia Vaccine Schedule

Canada Vaccine Schedule

EU Vaccine Schedule

UK Vaccine Schedule

US Vaccine Schedule

Impact of Vaccines

Vaccines save more than 4 million lives every year. 

Many diseases that used to be common, like measles, are now very rare because of vaccines.

They are especially helpful for protecting vulnerable groups such as children and elderly people.

Search by Ingredient:

Click here to search vaccines by ingredient

How are vaccines given?

Vaccines are administered in several ways:

  • Most vaccines are given as injections (shots) in your arm. These are called intramuscular injections because they are injected into the muscle in your arm.

  • Some vaccines (such as the rotavirus vaccines) are given as fluids that you drink, which is also called oral vaccines. 

  • Flumist is given as a nasal spray.

  • ACAM2000 is administered in a unique way that involves poking a drop of vaccine into the skin numerous times with a needle (to learn more, click here)

Vaccines in Pregnancy:

There are several vaccines that are routinely recommended in pregnancy:

  • Influenza (flu) if you are pregnant during flu season

    • Specifically one of the inactive ones so not flumist 

  • Tdap

  • COVID-19


Depending on the situation, other vaccines may be recommended to you, so talk to your doctor.

Live, attenuated vaccines (such as MMR) are typically not recommended during pregnancy.

Relevant terms:

  • Antibody: a protein made by the immune system in response to a foreign particle (antigen). These proteins circulate in the blood and help defend the body against the substance.  

  • Antigen: This is any substance that triggers the immune system to create antibodies. For example, allergens such as pollen are antigens. 

  • Attenuated: The pathogen is weakened but not completely inactivated. Attenuated pathogens are too weak to cause disease in almost all people. If you are immunocompromised, talk to your doctor before receiving vaccines containing attenuated pathogens.

  • Pathogen: a microscopic organism that can cause disease (usually a bacterium or virus)

Relevant terms


Last updated: Jan. 7, 2023

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